Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Voiding in board to BGA joints

Bryan She

#27517

Voiding in board to BGA joints | 5 March, 2004

Hello all, recently,I met a voiding issue in board to BGA ball joints. I've checked so many threads in this forum,but I can't find one which is really useful perhaps.Is there anyone who also met this issue,and then,in the end, succesfully get rid of this issue.I want some really useful information,that could imediatly make my joints free of voids. Thanks in advance Bryan.she@163.com

Bryan

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tommy

#27518

Voiding in board to BGA joints | 6 March, 2004

1)Solder paste selection 2)Reflow profile.Focus on soaking and TAL. 3)Moisture control for BGA. 4)Maybe the BGA solder ball already with void. 5)PCB design.Any via on bga land? 6)Solder masking type. 7)Solder paste volume apply on land. 8)IPC class 3 with 6% max void allow,class 2 is more then 6% and below 20.25%,class 1 below 36%(can't recall actual value).So,void is still allowed under IPC. 9)Last,try to get IPC-7095. By the way,there are many threads on bga void in smtnet. Hope above can help.

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Bryan

#27519

Voiding in board to BGA joints | 6 March, 2004

Thanks Tommy. In fact I've tried many types of profile,but it didn't work.I'll try to make the peak temp. as low as 205C and dwell long as in some threads Dave said.I've tried baking the BGA and PCB before mounting also dindn't work.yes,I've heard the volume of solder paste affects,so I'll have a try to change the aperture design.about the soldermask,I don't know how it can affect the voiding formation? Yes IPC allows some voids in the joints,but the joints have reached 25% area ratio of the joints.

Thanks

Bryan

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Ken

#27528

Voiding in board to BGA joints | 7 March, 2004

Increasing the metals loading may help. But may cause issues elsewhere. Unsure of your exact process....but may work.

Is anyone dispensing solder paste onto BGA pads...how is voiding in comparison???

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Vijay

#27529

Voiding in board to BGA joints | 7 March, 2004

Hello, Voids in BGA can not be eliminated. You can only minimize them by reducing the solder paste volume. Try to bake the plastic BGA's and PCB both as per the standard. Check the PCB at the BGA locations if the via's are masked.Masked via's results in additional voids. Thanks,

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Bryan

#27560

Voiding in board to BGA joints | 9 March, 2004

Hello everyone: 1.I use Kester R244 63/37 solder paste. 2.Stencil thickness 6 mil. 3.Springdale Chipset. 4.PCB finish:HASL 5.Profile:Peak temp.:210~220C,time above 183C:60~90 seconds,time between 150~183C 60~90 seconds. 6.Reflow oven:Heller 1800 Voiding happens almost on every boards,only in the joints of Northbridge to board.but not in the joints of southbridge. I've tried at least 5types of defferent profiles,didn't work. Baked the PCB and BGA before mounting,didn't work. voiding happens with either 5 and 6 mil thickness stencils. I tried molten the PADs on PCB in a solder pot for about 15 seconds,and then clean the pad...mounted with normal BGA components....Voiding as always. I tried removing the balls of BGA,planted with new 63/37 solder balls...mounted on normal PCB,can even see no voids by x-ray. I pried the BGA off the board,from the magnified picture,I found litter voids in the joints.and most of the balls attached to the PCB but not the BGA board.or,pads on PCB were ripped off,and I can see the base material of PCB. from above,it seems something must be wrong with the BGA ball.but it needs further study. it's very interesting that from the magnified picture,I found that,on each pad of BGA components,where solder ball were off,I found a hole in the right center.(I'll email you the picture if you leave your e-mail,coz I dont know how to attach one here)I can't tell whether they're via holes,or not...because from the cross-section picture,I can't find the via hole.whether these holes contributes to the voiding?or where do these holes come from?what should I do if all these voiding just because of the solder ball issues? BTW,I tried 3 types of solder paste,and found that,when use the RMA type solder paste,all voids disappear unbelievablely.What will happen if we use the RMA type solder paste with Cl content about 0.13%wt?and what are the concerns with use of RMA type no clean paste.

any inputs will be greatly appreciated.and thank you very much for providing any useful information or any articles about the root cause analysis. Thanks in advance! Bryan Sheh bryan.she@163.com

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#27579

Voiding in board to BGA joints | 9 March, 2004

Bryan: Comments are: * You're correct, solder paste formualtion is a major driver to voiding in BGA balls. * Voids are primarily process indicators. There is experimental evidence that voids retard crack propagation locally around the void on a temporary basis. * IPC-7095 defines acceptance critera

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Ken

#27590

Voiding in board to BGA joints | 9 March, 2004

What x-ray system are you using?

Check out Dage.

I bet you have voids...just can't image them. Why the fuss over voids? Voids terminate the crack propegation and can extend the time to failure for creep fatigue.

I would not be concerned unless your "egg-shelling" the joint.

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