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BGA drop off from the boards

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#72139

BGA drop off from the boards | 23 May, 2014

Hello all.

I need you advice and opinion on my problem with BGA drop off from the boards. Initial defect was ICT fail, but due to some accident, the board fell off, and the BGA just pop out. After some search, I end up to conclude it is a black pad fenomena (we are using ENIG finish). I examine the board with drop off BGA by using microscope. The BGA pad are all clean, and the solder and the BGA ball are both joint nicely (see attached picture). The reflow profile is within the solder paste's recomendation. There are 7 BGA, 6 of them are small pitch BGA (SRAM & FROM), 1 (droped one) is a controller/CPU (bigger pitch BGA). The other 6 BGA found no problem.

Please advice on this issue, whether correct this is a black pad issue or not?

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#72141

BGA drop off from the boards | 23 May, 2014

Hello,

these pads look so clean.....I am not sure you had a good solder connection there. I would check the following.

1. Is the part RoHS in a lead process 2. X -ray boards after reflow(I assume you will see head in pillow) 3. Check for board contamination and how the boards are handled. Check for part handling and contamination. Is it a moisture sensitive part? 4.Drill a hole in the board, attach a thermocouple and make a profile for this part exactly. Profiling might be your key for success.

I know that ENIG can have brittle joins, but this drop off test shows more than expected.

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#72142

BGA drop off from the boards | 23 May, 2014

Agree with previous comment regarding possible head-in-pillow. Use 3D x-ray or CT-scan to verify.

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#72144

BGA drop off from the boards | 23 May, 2014

I don't see any visuals that make me think of black pad phenomena. I do note that it appears that pads on the BGA itself have detached and been left on top of some of the solder balls.

To me it looks like the temperature profile is not correct, not enough temperature to melt all of the balls in the array.

As above, a Thermocouple beneath the part to use in your profiling process, should do the trick.

Good Luck 'hege

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#72147

BGA drop off from the boards | 23 May, 2014

Hi Evtimov. 1. yes both part and the process are lead free/RoHS 2. I ever did X-ray, the balls shape are good and I dont see any evident of head in pillow (but my x-ray machine is not too good) Head in pillow was also my first suspect. but after the bga drop off and I can see the ball have melted and joint together with the solder paste, then I remove the head in pillow. refer to picture attaced 3. For contamination (our process) it is very low chance coz the PWB are fresh (< 1 month) 4. for profile, last production was using a common board (not actual board) for profiling but the reflow seems good. Now, I'm making an actual board to confirm my reflow profile. But if the profile is good, then what is your suggestion? I'm thinking of contamination on the board supplier process. How do you think? Just for your information, I did pry 2 pcs of the mini BGA and 1 pcs of tantalum cap, all have good/strong joint. There are no brittle.

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#72148

BGA drop off from the boards | 23 May, 2014

Hi Hege.

I was not also too confident with the black pad (coz no black residue on the remaining pad). But based on my search on the internet regarding black pad. Most of them shows a very clean BGA Pad after peel off the BGA as the picture reference (same as my condition). That is why I come to decission this is black pad defect.

What do you think other than black pad will caused this issue?

For reflow I will perform another profiling using actual board.

For your information, after several days the pads looks oxidized (getting more darker).

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#72160

BGA drop off from the boards | 28 May, 2014

Just from the look of things (a picture) I would first guess it is a contamination problem on the PWB.

Check over all your handling practices. Make sure the PWBs are NEVER touched by bare hands.

I would not rule out the Black Pad phenomena, but it is so hard to tell from just a picture.

The picture that made me think of insufficient temperature is the first one, with the BGA device removed, but with what looks like the device pads themselves are sitting on top of the solder balls in one distinct area.

Might also be that the BGA is experiencing some warpage during reflow, possibly enough to lift a group of balls from the PWB at the peak, coming back to rest on the pad after cooldown. This of course would result in a less than strong attach, and possibly result in the drop off.

Interesting that the pads continue to oxidize. I wonder if this is an actual characteristic of Black Pad?

Best of Luck, let us know if and when you solve this puzzle! 'hege

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#72161

BGA drop off from the boards | 29 May, 2014

Edri,

if the profile is good for this part and everything else on the board looks fine, I would focus all my attention to the part. How is it packaged? How is it handled? Moisture sensitive - prebake if needed.If nothing helps, try another batch or even better - another vendor. It happened to me before to fight problems with a part and after I changed the vendor everything was fine. I think sometimes they don't handle the parts right and what you get is garbage. Regards, Emil

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#72163

BGA drop off from the boards | 29 May, 2014

whats the type of paset and the type of profile you're running. Doesn't look like enough heat to me on the first set of pics I see. Are you running ROHS BGAs on a lead profile?

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