Solving the thermal problems of HD2 or other snapdragon powered devices

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DTNT

Senior Member
Oct 17, 2009
60
2
Tashkent
Since yesterday I had the same problems. I feared it would be a slow decay from here and yet an other HTC device sent off to the bad repair center.

It seems my device had the freezes, but no reboots or such. When I looked at the cpu speed, it stayed at 1Ghz and didn't drop to lower speeds when idle. So I figured that would be why my battery drained super fast and the lower back of the device was getting hot. When I reduced the speeds manually, the freezes still did occur, but less frequent.

Today I read about a IMAP problem with Google mail. That problem was solved by Google and since today, there are no freezes, hot backs and battery drains anymore. When I force my device at full speed with a test, the freezes and stuff do happen again. So for me it was a false alarm. I hope the problems will stay away for now.

I also read about it, but is it also an issue on HD2 with Android on board?? My start freezing more and more in short times. With SetVSL app it works about 1 hour just with easy apps, with Angry Birds it is freezes at 5-10 minutes. With internet surfung (3g) it freezes in 3-5 minute. So, when I take out sim card and leaving device to idle, it can stay awake without freezes 1.5-2.0 days (upto battery). So what is a problem. Do I need to open my device and wear heatsink on as described in the beginnign of this theme?!
 
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ahmetsandal

Member
Dec 13, 2010
8
1
Dude, you succeed or not, whatever the result will be... I believe that you are doing a great job. You are trying to understand a real problem which htc and its suppliers deny. Great job, great effort... Additionaly, this is one of the best posts I've ever read: Whole post focuses on just the problem and the solution; there are no speculations etc. Thanks a lot.

PS: I have the same problem and I will be taking it to the service center tomarrow because I do not have appropriate tools to try. :(
 

motoi_bogdan

Senior Member
Sep 8, 2007
319
337
well once again i must issue a warning.

based on the nature of the problem NO AMOUNT OF HEAT DISSIPATION MATERIALS WILL HELP. PLEASE DON'T ATTEMPT THE GUIDE ON THE FIRST PAGE!!

The problem can ONLY be solved by resoldering the CPU using specialized tools. Even so, at this time i have a 50-50 success rate and without proper bga ball reforming tools, i cannot save a device that has failed because of improper reheating.

To put it step by step the problem looks like this:

1. you start using the phone, doing some intensive things on it.
2. phone starts to heat up, actually the snapdragon chip (mostly cpu + gpu) will heat up.
3. the solder points - about 180 small balls (ball grid array - BGA) will start to also heat up and ...well.. like all things that heat up.. will start to expand (dilatation).
4. the resin that fixes the chip itself to the motherboard will stay fixed, as it has a higher dilatation point then that of the solder balls.
5. as the balls underneath the cpu continue to heat up and expand, an increasing amount of pressure will form because of the outside resin keeping the chip unable to move along with the expanding balls underneath.
6. Over time the balls will start to crack - small fissures in their structure will appears - the balls are trying to expand in whatever direction possible. The solder points can also fail due to thermal/mechanical stress.
7. the small cracks will break the electric connection between the motherboard and the chip.. at witch point you get either a freeze or restart.
8. as the chip cools down - the solder points will contract and the cracks will be filled out, therefore the phone will work as the cpu operates normally.
9. over time, as more and more cracks occur in the bga matrix, the thermal point at witch the chip fails to work correctly will get lower and lower. Remember, it only needs one cracked connection (out of couple of hundreds) in order to stop working. You can get in a situation where the phone freezes at about 30 degrees celsius or lower.

Now let's say your phone does freeze at 30 degrees celsius. And let's say it's summer. There are 34 degrees outside. The phone is unusable. So in order to try to fix it, you dismantle it and attempt to fix it using my heat dissipation method. Well what you actually doing is sticking a piece of metal to the cpu chip. Does it address one of the 9 steps of the problem above? Well ... NO. That's because, when you assemble the phone back and try to use it, the piece of metal of sticked to the cpu will also get at room temperature along with other things there and the whole phone. So.. you will have a cpu at 34 degrees, a battery at 34 degrees and... a piece of metal at 34 degrees. The solder balls still have cracks and they expanded at 34 degrees, leaving the cpu to an unusable state (remember, my example stated you have a phone that freezes at anything above 30 degrees).
Simply put, if you simply place a piece of metal over the cpu, it won't solve the broken solder points and the original problem. In order to do this, the chip's solder point must be melted down to some degree, in order to fill out the existing cracks in the bga matrix. This is done using a smd heating station and it's very risky even in a service center. In fact some service center won't even attempt this - while faced with the real scenario where the cpu soldering melts in an ..unwanted fashion during the process (let's say 2 small balls melt and touch each other - a short circuit is formed underneath the chip).

I'm sorry but at this time this is the only real option. My first hd2 survived the procedure, so once done properly it seems that the fix effectively solves all the problems (i can use the phone at 50-60 degrees measured at the outer casing level - with absolutely no problem, freeze or restart). The second hd2 however died in the reheating process, most probably because of a short circuit in the BGA matrix.
 
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DTNT

Senior Member
Oct 17, 2009
60
2
Tashkent
My problems solved only this way!!! Get ice cubes from the freezer, put them into plastic bag, did like a cradle with this ice-cubed bag and put your HD2 on it. NO MORE FREEZES!!! Even with Angry Birds and 3G working and downloadings. But all this Happiness until ice melt down!!! XDA devs please find material that will last iced for a long time :). I think there is no options! So, now my HD2 has an accessory and it is - big 2 camera Daewoo Refregerator! Cool!!! Do you have one?!
 
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motoi_bogdan

Senior Member
Sep 8, 2007
319
337
well, this will normally work because you actively cool the device below the thermal point at witch you have problems.
Along with my reheating solution, designing an active cooling system can also do the job. But i don't see how you can stick a cooling fan inside the phone's casing. :D
Another more exotic way to do it is to mount a small peltiere effect cell inside the phone. This thing has the property to remove heat from one side of it and transfer it to the other side - when powered by a small electric current. In simple terms that's how it works but ... i don't know if it's possible to find a cell that small and another drawback is the constant power consumption of the peltiere cell.
 
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Hammerfest

Senior Member
Apr 3, 2008
1,682
286
San Antonio, TX
i cant afford shipping, but since its a dud anyway, id send u the HD2 mobo (only) if you wanted to take a whack at 66.6/100% success :p

Ill need to nuke it with simple green first to get of the thermal paste first :p

( a thought i tried was leaving the device on, wrapping it up, and purposely letting it overheat to extremes, and GOD DAMN does it get hot, i was sure a few more hours and the thing would have melted!!!! VERY BADDDDDDDDD, needless to say, it has worked on many a XBOX, but for the HD2.. sadly not!)
 

motoi_bogdan

Senior Member
Sep 8, 2007
319
337
i bought a whole hd2 from ebay. it had this and other problems and was sold as parts. I'm interested in the motherboard only. However, the shipment was not the problem, but.. customs in my country. I have to pay 24%vat + some 8-12% customs tax, all this applied to the value at witch i bought it from ebay. That's kind of expensive. I'm still awaiting the phone, will see what i can salvage from it when it arrives.

@Kane3162 keep the board. If i kill the new one, i could be interested in yours :D Right now i also can't afford to get another board.

aah, and i have one good looking eu hd2 and awaiting for a very bad looking tmous one. I'll be also looking to see how can i place a tmous motherboard in an eu phone (what needs to be changed since they aren't exactly compatible).
 
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Ev0luti0n_

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Apr 26, 2008
344
38
Portugal
OnePlus 8 Pro
facdemol: so i had an idea.... what about getting a spare case and doing some openings on it? sure a bit of dust will get in, but won't we be able to cool the phone a bit this way? Or even cut a large rectangle in the base of the phone and glue a "large" grid there, that will allow the phone to cool down, i think....

What do you think man?
and what are your advices about using an HD2 without problems so far?
sort of what things can you do that will diminish the problem?
 

motoi_bogdan

Senior Member
Sep 8, 2007
319
337
noup, a spare case with ...holes or anything like that won't work.

you're thinking the problem just as some computer cpu overheat problem. Like when you buy a quad-core cpu and cool it down with a stock sempron cooler, or something like that. In this example, the quad core cpu may overheat because of the insufficient cooling, so adding a bigger cooler, improving the airflow or stuff like that will work on cooling the cpu down. The ideea is that, the cpu was overheating due to an improper cooling system.
Regarding HD2, well it's a different story. The cpu itself DOESN'T overheat, it stays in the normal temperature range specified by the chip's manufacturer, Qualcomm. The CPU is design to handle such temperatures, even double the amount it gets by working on the HD2's platform. When the phone freezes or restarts, this is not actually the CPU that has failed. Even the 7 vibrate pattern doesn't directly indicate overheating. The trouble is.. the chip connection to the motherboard. It's made via a BGA (ball grid array) connection, using a low Pb. solder alloy. This is the part that fails due to heat generated by the chip. Those balls crack and the electrical contact they were making is now broken. The CPU "senses" this as a hard fault, it was simply processing some data and out of sudden it was stopped. Then if, the contacts aren't made at the next restart, it signals the fault via the 7 vibrate pattern.
If things get out of control and you get left with a phone that restarts or locks at about 30 degrees celsius, even if you stick a big computer cpu cooler on top of it, it won't help. No matter how big is your hunk of metal, it will still be at room temperature when you start the phone. And if this is higher then 30 degrees, no amount of passive cooling will do.

So in simpler terms, let's suppose you have a phone that locks at 30 degrees. There are 2 ways to solve the problem.

- stick a big active cooling system (fans, peltiere effect cells, water cooling) - a thing that can actively decrease the cpu temperature below the 30 degree level. Of course, not practical, whatever you get by doing this won't resemble a phone :rolleyes:

- remake the BGA soldering between the CPU and Motherboard. It's the logical thing, that's the place where the actual problem is located. This can only be done by either reheating the CPU with specialized equipment or actually removing it, remaking the bga (replacing the ball array) and soldering back the cpu, but that implies even more specialized equipment.
 
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Hammerfest

Senior Member
Apr 3, 2008
1,682
286
San Antonio, TX
yep, wish i had that equip... (and ypu can be sure as **** id replace the ****ty solder they used with the highest quality **** i could find...)

and for info incase u ever make the req, mines a TMoUS HD2 (of course)


@those who keep asking, the extra cooling will help... just not enough to even matter... the problem lies under the chip itself where the "thermal runaway" occurs... with the exception of a reball theres 0 recovery chance....
 

motoi_bogdan

Senior Member
Sep 8, 2007
319
337
i've updated post #1 with some pictures of the snapdragon chip. I've removed it from an eu hd2 board and i'm currently studying it and it's board for some future solutions for this problem.
The chip itself is pretty small, kind of 1x1cm and 3-4mm thick. :p Looks pretty geeky and smart.
 

Ev0luti0n_

Senior Member
Apr 26, 2008
344
38
Portugal
OnePlus 8 Pro
Thanks! so in the long term, will this happen to pratically all HD2, if not all? there are folks overclocking it to 1.3 on android! darn!

got start stocking some spare parts for me :D

facdemol: i still think that cutting holes in strategic places on the case would bring some extra cooling to the phone. I am not into electronics, beyond very basic stuff, but the more cooler the better, so... see my point? think about just a whole to extract heat with nothing forcing the air through. Not much, but something :)
 
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motoi_bogdan

Senior Member
Sep 8, 2007
319
337
not all hd2's will develop this. From what i see, tmous ones have better cpu soldering then european versions. But, i should state that i've only seen 4 devices so far. I do not have specialised equipment to test the solder material and it's properties, but from about 15 years of experience with soldering alloys it seems that the tmous ones have more led in the solder alloy and that makes the solder points a bit more flexible.
Anyway, i've received a broken tmous hd2 yesterday. Weird problem, because of cpu overheating some contacts that link the volume buttons (that flex connetor) to the mainboard and from there, underneath the cpu itself, were broken (short circuit). So if the phone is heating up, the volume button will go crazy and switch on by itself. Even if i disconnected the whole flex cable, the problem will still be present.
Well this particular hd2 was recovered after reheating the cpu, no more restarts or freezes but the volume control was broken after that. I remade the connection, by polarizing the common collector transistors that provide the voltage needed for volume switching. For switching the transistors i used the voltage needed to power on the green led (signaling charge completed) thus disabling this led. But i've got volume control and the ability to get into the bootloader. The phone was fixed this way.
No cooling system was attached (be it copper,mica foils or aluminum) , only the cpu was reheated.
So, it's now two working hd2's versus one dead hd2. Reheating is the only way as far as i see the problem now. I'm glad i rescued another hd2.
 
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ubejd

Senior Member
Jul 12, 2008
318
54
Gjilan
hi
a big thanks go for "facdemol" for his great share

i just want to share that i tried something... i went to a friend who has a bga rework station... first i just tried to rehoot cpu - i will make some tests and report here... if i dont succed i will try te remove entirely cpu and solder again ... i made some pic...







 
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motoi_bogdan

Senior Member
Sep 8, 2007
319
337
it's good if you have access to such equipment. Here are some tips, although the person who has that smd station should also know them.

Preheat the cpu from both sides, starting with the opposite side then switching to the front side (the side on witch the cpu is soldered). Don't use more then 200 degrees for preheating, the way i see it now, i guess only 180 degrees could be enough.

Try to be as quick as possible in the main heating part. It's better to heat it for some minutes, let it cool down, test it, then redo the process if needed. I never had success in one single turn and i also recommend to do the process in small steps.

Try not to use more then 360 degrees on the main heating stage. Compared to other chips, i find the hd2's cpu's soldering very easy to melt.

If you plan to remove the cpu, you will need some solder balls and a tool to form them on the chip's pinnout. I don't know the name of this tool in english but you really need to have it. Without it you can't resolder the chip back and as hard as i searched i didn't find any for the Snapdragon chips.

Good luck with the process.
 
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ubejd

Senior Member
Jul 12, 2008
318
54
Gjilan
Preheat the cpu from both sides, starting with the opposite side then switching to the front side (the side on witch the cpu is soldered). Don't use more then 200 degrees for preheating, the way i see it now, i guess only 180 degrees could be enough.
I did so...

Try to be as quick as possible in the main heating part. It's better to heat it for some minutes, let it cool down, test it, then redo the process if needed. I never had success in one single turn and i also recommend to do the process in small steps.
i will try again...

Try not to use more then 360 degrees on the main heating stage. Compared to other chips, i find the hd2's cpu's soldering very easy to melt.
for heating i tried 190 - 210 degrees ( Celsius )

If you plan to remove the cpu, you will need some solder balls and a tool to form them on the chip's pinnout. I don't know the name of this tool in english but you really need to have it. Without it you can't resolder the chip back and as hard as i searched i didn't find any for the Snapdragon chips.
he has some but those where for laptops graphic cards... we are searching for right one... i hope i could find otherwise we will have to improvise something ( if we could)

Good luck with the process.
Thanks ... we will need
 
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motoi_bogdan

Senior Member
Sep 8, 2007
319
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this is the snapdragon's back



as we can see, it seems that the pins are placed in a somewhat particular design, not evenly spaced, so other pin rows are spaced further apart from inner ones. Most bga are comprised of evenly spaced pins, it would be difficult to try to improvise. Also, most bga graphic chips have different pin spacing.
All in all, i guess that the idea is not to kill the soldering :D, it would be very hard to remake those connections.

Try to test after each round of reheating. I would recommend the first round not to exceed more then 1-2 min at around 360 degrees. It may look like you're not actually melting anything under the chip, but i'm a bit scarred on how easy that chip came off when i desoldered it. The ceramic cover (chip itself) seems to be very thermal conductive.
 
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    UPDATE -

    As of June 14. 2011 it appears the only viable way to solve this problem is to reheat the cpu with specialized equipment. I am currently testing if this can be done in a standard gas/electric oven (NOT MICROWAVE !!). If successful this method will solve the problem and the following guide (cpu cooling system) may help prevent it from happening again. Only building this cooling system is not enough and will not solve your problems.


    Hello dear members of XDA

    First of all please excuse my english, I will try to explain myself as well as I can. It will be a long post, it could be boring, it could be scary or whatever you like but bear with me on this one.

    So.. got myself a HTC (T-Mobile) HD2. A bit late in the game, but hell no, still a good phone. I've dreamed of having one but couldn't afford. Anyway finally i got one. A second hand broken one, damn it. :p
    As i found out the problem is pretty common: damn thing restart itself - thermally related - the old CPU overheat problem. By searching the net I found out that it's pretty common with some HTC models. HD2 has it, Desire has it, Nexus One has it, hell even some xperia models have it.. about half of the devices powered by anything from the Snapdragon series could have it.
    The problem could be easely described as : phone hanging, restarts, the dreaded 7-8 short vibrate sequence - phone locked etc.
    Mine was worst then i've seen on the forums or with other people. It locked itself for just about every reason i could get. Taking pictures, browsing the menu, using gps, the browser, 3g or wifi, watching a movie ... all concluded with restarts or lock-ups after some couple of minutes. I've found out that keeping the phone at 4-5 degrees celsius would solve my problems in most cases, but anything above 10-15 degrees would make the thing go crazy.

    Well, I'm pasionate about electronics, development in this area, trying to solve problems and things like that. Also experienced in heat and semiconductor related problems. I also had one macbook air that suffered from core shutdown because of overheating (also a well known problem for MBA rev 1.0) and managed to design an alternate cooling system that solved the problem. So i gave it a shot, i know there are many users that have similar problems and altrough i don't suggest them explicitly to make this hacks to their phones.. this is one way to solve the problem if you buy your unit second hand or don't have some form of warranty.

    So here we go.

    Big fat warning!!! Don't attempt these things with your phones unless you are familiar with the concepts or the tools involved in the process. Also, there is a real risk to permanently damage your phone. Not just real.. but big if you get something wrong.

    First step is to run some simple tests to determine the cause of the problem or the range it extends to.
    So, I used a multimeter with a K type thermal probe to measure the temperature of various components of the phone during intensive use.



    this is the back of the mainboard of my HD2. If you notice, HTC placed a blue-ish thermal pad over one metallic shield covering the back components. I don't know what's the purpose as the back casing in that area is made of plastic - no heat dissipation, or a bad one. Anyway that's a good place to place my probe. Some tape holded the probe in position. Because we don't have perfect mechanical contact between the probe tip and the casing or chips i expect +1 or +2 degrees celsius to be added to each measurement i will later describe.



    i now placed the battery over the back of the phone and secured it with some other tape and some toothpicks :D



    we're at 19.3 degrees. That's were we'll going to start from.

    there's a usefull little app that allows users to overclock or stress test their phones cpu. Found it here on XDA, i'll use it for some heat making purposes.



    as you can see.. we're already at 25.8 degrees, after 5 minutes of testing.. not to mention the actual heat making primary suspect - qualcomm chipset is on the other side. At 29.5 degrees at this point.. the phone locked itself. I reapeted the experiment 2 more times - got exactly the same result.. at least the readings were consistent.

    Ok, i then removed the motherboard to take some readings from the actual CPU.



    same procedure.. next readings. - at around 33.4 - 34.2 degrees (varies) on the CPU itself the phone will either restart or lock itself up. So you see how serious my problem is. Summer will come so I won't be able to use my phone... :p
    Measures have to be taken.

    Let's make a small introduction about heat related to semiconductors.

    Well, simply put a conductor (semiconductors act the same way) generates some amount of heat when an electric current is passed along it. This is because of the fact that small electrons moving along the conductor (in a simple way that's the definition of any electric current) will ocasionaly collide with the atoms of the material their passing through. In the collision the electron loses some amount of energy. That energy is heat. Also, heat itself can be described at an atomic level as the intensification of natural ocuring brownian movement of atoms. If they move a lot, if they are more agitated they create more heat. If they are more agitated, they are more likely to be hit by passing electrons. So a hot conductor is more likely to get even hotter because of that. There is a point were the heat generated makes the conductor's atoms prone to more hits from passing electrons in kind of like a geometric progression. That's called thermal runaway. It will tend to destroy electronics by overheating, melting or burning themselves up.
    Back to our phones now. The CPU produces heat. Because of the same effect described above. The heat in this case will either melt or break the small "balls" that comprise the BGA matrix on what these cips are mounted on. The small balls will either melt (extreme cases) or dilatate with increasing temperature. However it seems most of the new processors used by HTC are mounted in some epoxy resin that has both dilatation point and melting point higher then the flux and welding compound used to solder those cips. So the actual cip will tend to stay fixed in a particular position, unable to expand or contract with temperature variations, but the balls used in the BGA matrix underneath it will contract or expand with these variations. This could lead to a case when at least one of that balls (some couple hundreds in total) become "loose" or out of position, thus breaking the electrical contact it should have made. Therefore our problems. At fist large amounts of heat must be applied in order to actually break the bond between the cpu and board, but after that, once broken the tiny links are very sensible to temperature variations and they will expand or contract freely.
    Most users notice that at it's core, the problem seemed related to overheating (in the begining) but after time it's effects are degenerative.. phones seem to restart with no apparent reason. It's still overheating, but things are starting to get more and more worse as the chip and it's connections become more sensitive to heat variations. Thus, even small variations now produce these problems - my CPU restarts at 34 degrees .. that sucks.

    So, my only option was to try to reheat the cpu in the attempt to partially melt the broken "balls" in the bga matrix and hopefully.. i repeat HOPEFULLY they remake contact with the mainboard. A re-ball of this chip is not possible, as the resin placed around it by HTC doesn't melt at the normal temperature i could remove the chip itself, so heating it at even higher temperatures would risk killing the cpu long before the resin melts. Strange move by HTC to make things like this.

    Anyway.. here goes nothing..


    I've placed the usual aluminium foil designed to protect surrounding components by the heat generated by the rework station and the hot air used to heat up the CPU.



    I preheated the CPU for about 10 minutes, from both sides of the board, then switched to heating it at 360 degrees. I applied even pressure above it after it was heated in order to tighten the space between it and the board, just a little bit. THIS IS VERY RISKY. Normally not recommended because of the risk damaging the BGA. In this case the resin would prevent me from moving the chip to much so it's less risky. Not safe.. but less risky. :p

    I've let the board to cool on it's own for half an hour and repeated the temperature monitoring tests.
    Now i had an increase of maximum temperature before a restart from 34 degrees on the cpu to about 42. It's not much but it's a start. However above these temperature.. the phone will still lock or restart.
    I went for another round of reheating with the hot air station. After this, i've got slightly better results. Some 2-3 degrees more. My lucky break was when i suspected thermal runaway for the CPU. So i tried to make some sort of a heat sink for that chip using some mica foils for to220 can transistors, some thermal grease and a bunch of aluminum and copper foils. My theory was that heat dissipation will eventually accelerate faster above a specific level, a point from witch thermal runaway occur. In my case in the initial tests, even after the phone locked itself and i manually restarted (battery out - in) the temperature continued to increase even faster altrough the phone wasn't doing anything intensive.
    The role of my "heat sink" would be to dissipate more heat rapidly and in some manner to press the cpu against the board.
    After I placed the mica foils directly above the cpu with thermal grease above and beyond i mounted back the metal shield over that area. On it, i placed some more silicon paste and some thick copper foil (used in some broken laptops i have over here). It looks ugly but.. worth a shot:



    after that i begin making the rest of the heat sink using aluminum foil. I folded about 12 layers, between each of them having placed... more thermal grease and at the 6-7 layer another round of mica crystal foil.

    Here's the aluminum foil



    I then pressed the foils very hard between two flat surfaces in order to remove the excess thermal grease.
    I "anodized" the first layer (the one in contact with the cpu shielding) with some ferric chloride. Before that, the board looked like this:



    After the logic board was mounted back, i remade all the connections and after some preliminary tests, mounted the phone back together. It now looks like this



    I only have to re-attach the serial no. and imei, plastic sticker.

    Of course i then run tests. I heated up the phone with a hair dryer to simulate a hot summer day. About 40 degrees, just to be sure. I then run cpu stress tests and a full divx movie (impossible in the past). On preliminary testing, i had indications that i avoided the thermal runaway the cpu now running stable at 24 degrees (19.3 in the room - ambient temperature). No more, heating up by itself to about 40 degrees then restart.
    On the final testing, with the phone put together, i heated it with the hair dryer and achieved 40 degrees. I started it and run stress tests. No more lockups or restarts, not even a single one. However with the phone put together i can't measure inside temperature on it's components. As i feel it, it get's warmer, it heats up to some degree, but now it's spread all over it's surface. For some particular reason it doesn't restart anymore.

    I then tried, cpu stress test, wlan connection, pc connection and browsing the net all at the same time. NO RESTART :D I watched a full 1.30 hour movie at max playable quality, the phone was really hot (43-44 degree at it's surface) but still no problems.
    It appears that for the moment i saved the phone. However, future behavior is still to be determined.

    I'll get back with more testing, in the following days and eventually i hope to devise a general method for building heat sinks for phones (yeaah, ridiculous....) using combinations of metal and thermal conductive cristals. The ideea is to find out if reheating the chip by hot air station can be avoided (this involves the most risk). But the start is promising. By the time warranties will expire and phones like the new droids or winmo 7's start to break from thermal problems, maybe i'll have some sort of a more user friendly solution.

    EDIT JUNE 04.2011
    since i have a dead hd2 motherboard here, i tried to remove the cpu to expose the BGA soldering. Just for fun, no chance of BGA reball, as there aren't any tools available for this particular chip. The resin prevents a proper removal, at about 450 degrees celsius it was still kind of hard, so i had to forcefully remove the chip and break some of the BGA. The chip is very thin, kind of like a micro sd card. It heats up pretty quick and fast, the solder points underneath it got melted in about 2-3 min at 370 degrees celsius.
    Here's how it looks.
    This is the motherboard without the chip. The BGA matrix is broken, some balls were simply ripped out when i forcefully removed the chip.



    This is the actual chip compared with a mini sd and and standard sd card.



    ...and this is the underside of the chip. belive it or not, the chip is actually alive and it's pins are ok. It cannot be used because it cannot be properly soldered to a board. Guess i'm gonna punch a hole through it and use it at my key chain, along with a laptop cpu already there ;)



    In the following days i will experiment with the solder points&materials in order to try to produce a more safer method to reheat future boards with thermal problems. It seems this board died because of overheating and a short circuit made over the center of the array by 3 solder balls that got in contact once they were melted.
    4
    the mica crystal pads should be available at any electronic components store. If you can't find any, you could try to substitute them with any other similar purpose material. Use only thermal pads used in electronics for semiconductor (transistors mostly) thermal dissipation. However from what i know or can test, the mica ones are superior to other designs or materials.
    Also, good quality thermal paste is a MUST. Cheap one tend to dry out or loose effectiveness over time.

    @ profahmad - yes, the back of the lcd unit is metallic. Normally it was not intended to provide heat dissipation, neither is in direct contact with the heat making components, but it takes some of the heat and spreads it over it's surface. What i did is to forcefully use this piece of metal along with the materials i used for the "heat sync" in order to facilitate better thermal dissipation. The HD2 is build on the "edge" as you can see, even if the display unit is removed or improperly mounted, the small effect in cooling the board it once had is enough now to provoke some of the thermal issues.

    @januszgorlewski reheating is very risky without solid previous experience. Simply reheating the cpu didn't solve the problem for me, it only ameliorated it a bit. The new heat sync did the trick so i suspect you can skip reheating with not much of a loss in effectiveness. However i should have experienced with more devices in order to know for sure the effects of each stage of my experiment.

    @sqeeza yes, a petition could be filed out. However, there are 20-30 topics in this area about hd2 freezing or restarting but most people don't know there is a thermal problem related with these events. If we advertise the problem and it's cause to these people they could run some simple test to determine if their phones are also suffering from this problem.
    4
    first of all heating up the qualcom chip is recomanded as a last resort option. however if you reheat it, pressing the chip to the board is VERRY dangerous, as it could permanently damage the BGA connection.

    Here's some sort of guide on doing this. You will need a screwdriver, some 4-5 mica foil pads (you can get them from any electronic component store (get them for either TO3 or TO220 casing and cut them to the size of the cpu inside hd2) some good thermal grease (arctic silver or something for pc cpu's) an aluminum sheet for you to cut a piece of it.
    * i don't recommend silicon thermal pads, use only mica crystal pads
    * you can substitute the aluminum plate with aluminum/copper foil - the first is the one used for food wrapping)
    * i don't recommend using anything beside a smd rework station (either hot air or infrared) to heat up the board. Although a heat gun can develop high temperatures, the air debit is to high (dangerous, you can blow up other components) and you will lack precise temperature control needed for this job.


    1. Disassemble the phone following HTC's official videos. Completely remove the motherboard from the phone's casing.
    2. Once you have the motherboard de-attached remove all metallic shields on both sides. Normally these prevent EM interferences from the outside to get in and mess with electric signals over the PCB. We can use them as part of the "cooling" system later.
    3. OPTIONAL - efficiency yet to be determined/great risk involved - use either a special oven (not microwave !! it WILL kill the phone!) or a smd rework station to pre-heat the mainboard. Temperature must be set at around 95-110 degrees. Board must be heated from both sides, or at least one at a time, beginning with the one opposing the cpu side. Let it preheat at least 10 minutes.
    3a. after preheating, use an aluminum foil to cover the rest of the components, anything other then the cpu itself then get to the actual heating, switching first to 250 degrees and directing the air stream on the cpu itself (using a larger nozzle for the tip of the heating gun). After 2-3 minutes of 250 degrees, swich to 340-360 degrees and heat the chip for another 5minutes. Move the heating gun around the surface of the chip and try to heat it evenly. If you have the guts and you are crazy enough use a knife with a larger blade and put the tip of the blade in the hot air stream in front of the cpu. Let it heat for a while, and also, continue heating the cpu. When the blade tip is hot enough press the chip with it , starting from the center and following each side. Apply even force on each press and try to have the blade as parallel with the chip possible. Don't press too hard, if you haven't kill the chip yet, that will kill it.
    3b. let the board to cool down on it's own and during cooling try not to move it or do anything to it.

    4. place a little amount of thermal grease on top of the cpu then place 1-2 mica foil pads (depending on thickness) over the cpu. Gently press the mica foil with one finger over the cpu. Now place more thermal grease over that mica foil and try to place the metalic shield over that area. If successfully done, the metallic shield should be in contact with the mica foil and the grease. Place back all shields on the main board.
    5. On the phone's casing, measure the back of the display and try to cut an aluminum sheet of exactly the same size. If the sheet you can find is too thick - polish it and place it in a solution of either caustic soda or ferric chloride. This will get it thinner, but you have to supervise the process as if you leave it for long, the sheet could get completely dissolved. Check the sheet on short intervals (1min) to see the progress. Always use gloves and eye protection as both substances are dangerous (never mix them, use only one of them, the one you can get or already have). Once done, you will have a thin aluminum sheet that's flexible and about 1mm thick.
    6. notice there are some ribbons connecting the display to the motherboard or other exposed metallic contacts. Before placing the aluminum sheet over the display's back, place some insulating tape over those metallic contacts to prevent any shortcircuit forming between them and the aluminum sheet. Next place the aluminum sheet over the display's back. Be careful not to damage any connector or ribbon in the process.
    7. place more thermal grease on the cpu's metallic shield and check to see if the motherboard gets in good thermal contact with the aluminum sheet you just placed over the display's back. If there is still some space between them, use another mica foil and place thermal grease on both sides of it.
    8. reassemble the phone, and make some tests to see if you get some improvements.

    One more thing, this little project of our is in a "more to be seen/tested" state. As of now... only one device was fixed by this method - mine, it could have been simple luck. I don't know yet. :p more then a week later (strange weather also, + 20 degrees outside then last time i wrote the original post) the phone still works ok. Now running 1.3Ghz overclocked with NAND Android


    @ januszgorlewski i remember the first time the phone was vibrating 7 times and i didn't know about this problem, i though it was an WM6.5 Energy Rom feature :) .
    3
    as i found out until now the steps from a good working hd2 to this problems are something like this:

    1. phone working ok. mainboard (lower part of the device) heats in some conditions - demanding programs etc battery can reach about 40-45 degrees max. without problems. The phone will restart or freeze (cpu halt) in any of these situations :
    - battery temp exceeds 45 degrees and stays over this value for at least 5-10 minutes in order to trigger the thermistor used to measure the temperature in this area over i2c. at this time, it will prevent further charging and restart or lock the phone. This is normal behavior.
    -CPU exceeds 60-65 degrees (exact value still to be determined. i'm trying to get acces to some similar chipset datasheets). This produces CPU halt. Depending on what you're doing, the halt will either reset the phone or simply lock it up. Restarting by soft reset or by itself will probably return the user back in the home screen with the phone still working. This is also normal behavior, related to qualcomm chip.

    2. phone starts to malfunction. This condition starts by either large variation in temperature - mainboard al low temperature gets fast to full load or simply sustained full load. All HTC HD2's revisions have the same type of soldering in the cpu area. Visually speaking (no conclusive data yet) first revision used a bit more epoxy resin to secure the cpu in place. In the context of overheating and solder balls dilatation, that's not quite a good thing. Some sort of thermal spike must occur in order to break the contact between cpu and motherboard. Warning, if your phone will lock up and doesn't restart by itself, it's imperative that you disconnect the battery because as I measured, even with the phone locked, the CPU still overheats even more, thermal runaway occurs and temperature climbs to dangerous levels. I never left the phone do this for a long time, therefore I don't know how much it will still overheat, but it does and it will. In the initial stage of the problem, only extended heavy load use can trigger the problem. A common case is keeping the phone on in the car and using it for gps navigation in a hot summer. If the phone will restart before either 45 degrees at battery or 60-65 degrees at cpu level (however the last one is harder to measure) then you certainly have problems and they are just at the start.

    3. problems get worse. At this stage it is possible to notice the 7 short vibrates at boot time if the phone is warm or kept in a warm environment. You don't have to push it very hard, it only needs to be warm. The vibration pattern is an error code made by the actual qualcomm chipset, not sent by either bootloader, spl or operating system. When in happens the cpu will lock itself up, however file transfer (including nand memory acces, storage card acces and basic operations) or other chipset functions will still work for some time. It appears only cpu processing is being halted. So if this occurs when you boot the phone, it will lock up, but if this occurs when you are flashing a rom, you might continue to see the progress bar still filling. The vibration pattern signals a physical damage to the qualcomm chipset has ocurred. There's no way around it, when it occur it will never just .. heal up by itself.
    You will notice that the temperatures needed to induce a restart/lockup will decrease with time (both battery & cpu).

    4. Problem at it's worse. CPU can lock itself even at 35-40 degrees (measured at it's level). Ambient temperature of only 10-12-15 degrees is enought to have the phone experience problems. The cpu start to suddenly produce either lock-outs or hard faults or simply work intermittently. The OS may give errors relating ARM CORE failure or fatal errors regarding execution of certain "lines" (related to code lines in the os core programming). At this stage, the phone doesn't need to feel warm in your hands to produce these problems. This could trick some people not to still relate this to thermal problems and look for the solution or problem cause elsewhere. It's still related... but at it's worse.

    5. Total CPU collapse. If the phone locks and remains locked in whatever screen or program it was running, like i've said before, it will still overheat. If a stage 4 phone is left overheating, chances are that more balls connecting the chipset to the motherboard will fail. If any one needed to correctly initialise the chip or to power it on, fails - then it's end game for that phone. It will simply stop working and never turn on. Some other variants are that the phone will only start if placed in a freezer or start but never complete a boot sequence (either os or bootloader .. or both could be unable to start)
    3
    yep.. more than 2 weeks have passed and after i completed all possible tests the phone still works ok.
    About 22-25 roms flashed (wp7, wm6.5, android, ubuntu) phone was used either normally or heated with a hair dryer. At about 30 degrees ambient room temperature, i run some 720p testing and manage to run sample videos until battery died out, then rerun the videos while charging (charging induces more heat also).
    In all those 2 weeks i had only 2 restarts, both in wp7 (can't remember what rom version did that) and both occurring when i was setting up the phone after the phone update. Phone was cold however. I didn't manage to produce more restarts either when the phone heated up or i tried running intensive apps on it. Guess it was software related.
    So.. i guess it's over with this problem.