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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


KZags

#10376

600 pin BGA Reliability | 27 July, 1999

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.

reply »

Earl Moon

#10377

Re: 600 pin BGA Reliability | 27 July, 1999

| 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

reply »

APE South

#10378

Re: 600 pin BGA Reliability | 27 July, 1999

How many layers is the board....

Is the BGA ceramic or plastic?

Dave Kennedy APE South apecorp.com

reply »

Justin Medernach

#10379

Re: 600 pin BGA Reliability | 29 July, 1999

| 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. | Kathleen, After reading what you have written so far, I have a few comments for you. First of all, don't let the pin count of a bga intimidate you. From 48 pins to well over 1000, it's all the same. Have a good profile and a good print and you'll get decent product. This however, is not your issue. You are certainly correct in being concerned with localized warpage causing issues. .062" thick for a board that large is fairly daunting. You're definitely going to run into warpage issues unless you use a stiffener or have center rail support on your oven. I'd also like to make you aware of handling after processing. The amount of additional stress on the solder joints is dependent upon the location of the component on the PWB. The closer the component is located to the center of the board, related to travel through the oven, the higher the strain on the solder joints of the BGA. This strain will be manifested only slightly after reflow but think about when the PWB is mounted in it's chasis. No chasis has tooling/mounting holes designed for a warped board. They are designed for a flat product. When this product goes through box build, the strain on the solder joints will be at its' maximum. When these boards exit the oven, place them flat and let them cool. After the boards have cooled, handling is critical. Don't bend or stress them in any way. Your one saving grace is the high pin count. If this is a eutectic balled component, the stess will be spread out over 600 pins which will lessen the stress per solder joint significantly as compared to a 352 pin device. If you run into problems, a stiffener is your answer. I've had to process boards before by printing, mounting a stiffener after printing, and then placing all components. It's a pain but yeilds a stable product.

Regards, justin

reply »

PCB Soldering Tools

Plasma Prior to Conformal Coating