| I'm working on a prototype board that requires a 600 pin BGA. This is a metal top BGA being placed on a 11" x 17" PCB about .62" thick. | | The part is 1.77" square with a 50 mil pitch and 30 mil bump diameter. The bumps are located on the perimeter of the part only. | | I'm worried about localized board warpage in the area of the BGA stressing the joints. The board will be a dual reflow but the BGA won't be placed until after the first reflow and we don't have any problems currently with board warpage. So I normally wouldn't expect any problems, but something always seems to sneak in. This part is much larger than anything else we've placed and not very forgiving so I want to make sure I've investigated all the possible ramifications. | | Any insights would be appreciated. | Thanks. | | At my last assignment, the company's process development team provided reliability data including up to 600 ball SBGA's. Under effectively process controlled conditions, with properly constructed MLB's, they said no problems. However, the largest perimeter device we used in production was a 432 ball device - on a routine basis. Again, under controlled process conditions, with large properly constructed MLB's, no problems were encountered. I can only assume success very likely because of testing and because a SBGA still is plastic with a metal top, therefore offering considerable compliance under thermal and mechanical stress - to some degree.
On my current contract, we use CCBGA's with over 1100 columns and encounter some difficulties associated with such large devices on very large and high layer count MLB's. Of course, column arrays have more compliance than "normal" BGA device types as "true" solder joints are formed during processing.
Earl Moon
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