How to: CPU Socket Reflow

[jbonetwo]

Continuing from this thread

I am going to attempt a cpu socket reflow as a last resort to try and fix this motherborad: ASRock 970 Pro3 R2.0

I've got the gist of the procedure. Do correct me if I am missing anything.

1. Cover everything but the cpu socket with aluminum foil

2. Use pen type flux to flux the area around the cpu socket and let if flow between the socket and motherboard.

3. Use heat gun to heat the cpu socket to ~200^C.

4. .........

5. Profit!

Questions:

1. Won't the CPU Socket itself melt at 200C?

2. Won't the solder at the back of the motherboard melt?

[Th3_uN1Qu3]

Re: How to: CPU Socket Reflow

It will melt with hot air. The only solution possible with the hot air gun would be to reflow it from the underside.

[jbonetwo]

Re: How to: CPU Socket Reflow

Please keep in mind that I have never done anything like this before.

A step by step how to for dummies would be very much appreciated!

[momaka]

Re: How to: CPU Socket Reflow

I've got the gist of the procedure.

Looks so to me as well. I'm just going to add a bit more details or tips if I have any on some of the steps. I don't think I have an exact step-by-step process, since there can be set-up and tool availability variations.

1. Cover everything but the cpu socket with aluminum foil

It's a good idea. But it's better to just put a "wall" of aluminum foil just a few centimeters around the CPU socket and not cover anything (except possibly capacitors, if there are any that are too close to the CPU socket).
Also, do something similar on the under side of the boards as well - at least if we are going to reflow from both the topside and the bottom side (more on that in a bit).

2. Use pen type flux to flux the area around the cpu socket and let if flow between the socket and motherboard.

Good idea. But since there is great variation of fluxes, and they all perform differently, I would recommend you first put a little bit of that flux on the surface of a broken/junk motherboard and a piece of solder next to it. Then blast it with your heatgun and see what it does. Ideally, you'll want the solder ball to melt and the flux to still be active. Some fluxes (especially cheap liquid fluxes) will just boil/sizzle and leave a brown residue way before the solder melts - you don't want this! Such fluxes are only good for general soldering, but not for reflowing/reballing and BGA work.
One flux that I can recommend to you that is very decent for BGA work is Kingbo. If you can find smaller quantities so that you can find it cheaper (generally, it comes in 100g jars), then definitely get some. It's not like the 100g jars are overly expensive and you can use it for any type of solder work, but still something to keep in mind.

3. Use heat gun to heat the cpu socket to ~200^C.

This appears to be a post-RoHS era motherboard, so it likely uses lead-free solder. In that case, you would need to get the solder up to at least 220C (around 230C is best, but don't exceed 250C as some components will not take the heat too well).
If you are using the bog-standard type-K thermocouple that came with your temperature meter (assuming you got one), then keep in mind that it will take some time before the thermocouple picks up with the board temperature. Generally, the larger the thermocouple, the slower it will respond to the heat changes. So by the time the board has reached 230C, you may as well have some areas reach 240C or higher if the thermocouple is big. Just keep that in mind.
Last, and most important, I would recommend you heat the board from both sides to avoid warping. The easiest way to do this is to put the board on a oven-type grill or some kind of metal screen and suspend that off the edge of a desk or table. This will give you access to both sides of the board. However, make sure the grill/screen is solid and won't warp from the heat or allow the board to warp from the heat (add aluminum foil balls as supports as needed around the CPU socket). Once you have that set up, start heating the board from the bottom. Make sure to move the heatgun nozzle around so that it doesn't create hot spots or end up overheating certain areas... At around 150C+ temperature near the CPU socket, you may stop the heating and proceed to adding flux around the CPU socket (but make sure you don't get any in the socket!). Putting flux on a hot board is better, because the heat will suck the flux under the socket. After this, go back to heating the board from the bottom. When it reaches around 180C, move to the top side and heat the CPU socket from above. Go all the way until at least 220C (as mentioned above). Once you do, hold the temperature there for about 10 seconds, then you can turn off the heat and let the board cool.

Alternatively, if you don't have a grill or metal screen to put the board on, then put the board on a flat surface and add aluminum balls as supports - especially around the CPU socket. This is done to prevent the motherboard from warping from the heat. The repeat the above procedure, but by only heating from the top side.

1. Won't the CPU Socket itself melt at 200C?

Shouldn't unless you heat it up way too much. It may become a bit more yellow, though.

2. Won't the solder at the back of the motherboard melt?

Yes, but that's a good thing. It means that the solder under the CPU socket has successfully melted as well (so higher chances of the reflow being successful).

[jbonetwo]

Re: How to: CPU Socket Reflow

Thank you momaka once again- thats exactly what I needed.

Just a couple of points to clarify before I work on a test board.

1. Kingbo flux is hard to find on amazon, and it appears to have the consistency of paste. Wodnering how I would apply it to a flat, extremely hot board.

2. Kester is the flux I'm currently looking at. But again, one wonders how to apply it to a hot, flat board despite a foam activated tip on the pen.

I guess it would be ok to tilt the board 90 degrees with heat resistant gloves for the flux application and that this wouldn't cause too much warping.

3. How would one, if necessary, clean out the excess flux runoff?

4. About the 'solder melt' at the back of the board. I suppose I'm expecting it to drip or at least run to any surface it is in contact with.

Will be moving to test phase on a dead mb for practice once the flux and thermometer arrive.

[momaka]

Re: How to: CPU Socket Reflow

Wodnering how I would apply it to a flat, extremely hot board.

Easy. The flux will go under the CPU socket all by itself due to the heat (don't ask me how it works... it's magic to me, but I know it works), so you do NOT have to tilt the board at all. This applies to both paste flux and liquid flux.

The Kingo paste flux I have in a medium-sized medical syringe.
I've heard/read good things about Kester, so I think that should be fine as well. I'm not sure how the foam-activated tip on the pen works. I guess you may have to apply it to the board before heating it up to possibly avoid damaing the pen's tip. But again, you need not tilt the motherboard. The flux will flow all by itself as you start heating up the motherboard.

3. How would one, if necessary, clean out the excess flux runoff?

After reflowing the board and letting it cool sufficiencly (i.e. cool enough to hold), you may use IPA (Isopropyl Alcohol). Acetone may work too, but I don't recommend it due to it being "harsh" to some plastics.

4. About the 'solder melt' at the back of the board. I suppose I'm expecting it to drip or at least run to any surface it is in contact with.

It won't drip, or even move at all unless you really really do overheat the board and/or accidentally bump it very hard when it's above 220C. Components on the underside won't fall off either, so don't worry about those either. Just avoid bumping the board when it gets very very hot in the reflow process.

[jbonetwo]

Re: How to: CPU Socket Reflow

Great! Feel confident enough to do the job properly on a test mb. Thanks again!

[momaka]

Re: How to: CPU Socket Reflow

No problem .
By the way, I forgot to mention... it's also probably a good idea to wear safety glasses when doing this.
Although I've never had anything explode or hit me in the face (and I've done many many reflows/reballs), I still recommend them just in case. After all, you only have two eyes. Better be safe than sorry.

[jbonetwo]

Re: How to: CPU Socket Reflow

Will do, thanks!

[jbonetwo]

Re: How to: CPU Socket Reflow

In preparation of the reflow, I notice that the cpu does not sit flat in the socket of this motherboard. This is unlike the same replacement motherboard and an older generation asrock m3a770de.

Difficult to take a picture here because of the low height and obstructing caps around, but let me try to explain.

If you place the cpu in the socket, and apply pressure to one corner with your fingernail, there is movement, whereas on the good motherboards, there is no movement.

I guess all that tugging and pulling on the hsf owing to the un-cured TIM did something here.

Wondering if a reflow would fix such an issue or make it unfixable. Or if i should apply pressure to the socket once it reaches 230 degrees C.

[jbonetwo]

Re: How to: CPU Socket Reflow

Alright. Took off the retention bracket and that gave me some room for pics. Apologies for the angle on the faulty mb but there is a cap bang in the middle of the line of sight.

You can still see the cpu lift when very little pressure is applied to one corner. On the good mb, there is NO movement whatsoever.

CPU in ASRock 970 Pro3 (faulty) normal and with pressure applied to one corner:



CPU in ASRock M3A770 (working) normal and with pressure applied to one corner:




This is after applying a vacuum cleaner to the socket...

[momaka]

Re: How to: CPU Socket Reflow

Or if i should apply pressure to the socket once it reaches 230 degrees C.

No, never apply any pressure to the socket when it's hot. You'll either crush the balls and bridge them or move the socket. At 230C or above, the solder will melt and the socket should drop to where it needs to from its own weight.

As for the CPU not sitting even on the socket - I can't sure if that's the problem or not. All I can say is that I've seen this a few times on older AMD socket A motherboards, and it has never been an issue. In fact, I think one of my S939 boards did this too, but I don't remember too well.

[jbonetwo]

Re: How to: CPU Socket Reflow

Quite a few hiccups with the test motherboard.

1. The foam activated tip on the flux pen is terrible and does not release enough flux.

2. The flux does not run through the socket to the other side as i supposed it would. Looks like i will have to apply it to all four sides.

The only flux i'll likely get here is paste type. I hope it will be enough to smear it on all four sides at 150C.

3. The steinel heat gun would not raise the board temp above 115C on high though it is rated at ~500C. There are 2 probes on the thermometer so i've attached one to the top and one to the bottom. I'm measuring the top temp when heating from the bottom and vice versa. I know that some heat will be lost to convection but this heat gun is obviously faulty. When pointed directly over the probe, it registers max of 160C.

Since this is the only heat gun available here, I'm going to play it safe and get one rated at 600C from abroad which will take about 2 weeks.

4. The probe that is taped to the bottom with aluminum tape keeps coming off due to a combination of hear, air flow and gravity. Looks like I'll have to use the top probe only.

[Th3_uN1Qu3]

Re: How to: CPU Socket Reflow

The probe won't be an issue. I always use probes on the top only. If it works for reballing and replacing chipsets, it'll work for anything. The top temperature is what interests you, as the connection you are trying to reflow is on top of the board.

[stj]

Re: How to: CPU Socket Reflow

check page14

[momaka]

Re: How to: CPU Socket Reflow

3. The steinel heat gun would not raise the board temp above 115C on high though it is rated at ~500C.

Try this:
Cut a piece of solder and place it on a surface that doesn't burn. Blast it with your heat gun and see if it melts. It may take several minutes for that. If it doesn't, then the heatgun really is too weak. If you do buy a new heat gun, do the same test for it as well. This should give you an idea more or less of how hot or powerfun the heat gun is.

4. The probe that is taped to the bottom with aluminum tape keeps coming off due to a combination of hear, air flow and gravity. Looks like I'll have to use the top probe only.

Just place both probes on the top side, but on opposite sides of the socket. Also, don't put them on the socket but a few cm to the side of it. That way, when the temperature from the probes reads about 220C, you'll know for sure that the socket has reached at least 220C as well. Go for 225 to 230C.

[jbonetwo]

Re: How to: CPU Socket Reflow

The probe won't be an issue. I always use probes on the top only. If it works for reballing and replacing chipsets, it'll work for anything. The top temperature is what interests you, as the connection you are trying to reflow is on top of the board.

check page14

that is some useful info there, thanks!

Cut a piece of solder and place it on a surface that doesn't burn.

I did not forget to try this. the air from the heat gun kept blowing the solder wire off the board so i gave up.

tried it again just now with a piece of solder wire propped up against the cpu socket on a dead motherboard. blasted it with the heat gun till the board started to make popping sounds :S.

the wire curled into a ball fairly quickly and was malleable at the end but it did not melt in any sense of the word.

[sanehdeep2012]

Re: How to: CPU Socket Reflow

very healthy discussion i learn new things thanks momka and stj for your valuable details and

[larrymoencurly]

Re: How to: CPU Socket Reflow

The only solution possible with the hot air gun would be to reflow it from the underside.

Would it help to remove the plastic on the top side of the CPU socket so more heat can transfer from the pins to the solder bumps?

[dj_ricoh]

Re: How to: CPU Socket Reflow

don`t!