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BGA faults



BGA faults | 17 August, 2000

Hi Folks, Hope yous can help. I'm having a problem when reworking (placing) 40mil BGAs. One side seems to be collapsing more so that the other, resulting in the outer row of balls not properly reflowing and making the connection. This is only happening on certain PCBs within the same batch. I'm using a SRT rework machine and the thermal profile is within the reflow criteria, as some cards are placing and reflowing well. My suspensions have lead to coplanarity problems associated with slight twist within the larger/ dense PCB substrate. (although this is difficult to see) Does anyone have any thoughts on the cause of the problem and if it can be solved.

Would be much appreciated,

Cheers Jacqueline

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Re: BGA faults | 17 August, 2000

Sounds like improper heat distribution! Raise your prheat/soak time to assure even heating of the board∂. Another issue could be the moisture causing this anomaly.

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Re: BGA faults | 17 August, 2000

Thanks for your comment; if it is an unbalance heat distribution, why is it reflowing some cards with the BGA?? If it was a incorrect thermal profile, wouldnt they all be displaying the same problem? All boards & comps are being baked prior to rework.

Cheers, Jack

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Re: BGA faults | 17 August, 2000

Hi Jaqueline,

my first thought goes into the same direction, twist or warp (either the board or the BGA itself). I don�t know the SRT equipment. I�ve noticed with our equipment using a spot underheat element caused some warpage of the PCB making it almost impossible to maintain correct alignment for 20mil buggers and something quite similar to your experience with BGA. I�ve seen those effects occuring during normal reflow and lucky as we are we can watch the whole thing happen in our vapourphase and they are due to noticeable warpage of the PCB. So if your problem can�t be solved with proper and even preheating of the board the cause might be with the boards itself although they come from the same batch (we see this happen occasinally).

Ultimately you have to find the cause somehow to take the adequate measures.

Good luck Wolfgang

PS: How about the treatment of the BGAs? PBGAs trend to warp themselfes. I left some samples open for a couple of weeks. Next time I showed them in a workshop they were real rockers.

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Re: BGA faults | 17 August, 2000

Again me, how about your room? Someone opened a door or window. Encountered that nasty influence with my old IR reflow system.


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SMT Tech


Re: BGA faults | 25 August, 2000

Is it board specific? If so I used a piece of sheet metal between the board and the heaters to correct a similar issues, where a ground plane was absorbing the heat.

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