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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