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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Alan Pestell

#15979

BGA underside cleaning | 7 May, 1998

We are about to use BGAs on our equipment. We clean all products prior to confomally coating them - to keep moisture off the IC legs. Will this be a problem with BGAs. Will we need to get the coating underneath the BGA or will the pitch on the balls be sufficient to prevent problems ? Any comments appreciated.

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Terry Burnette

#15980

Re: BGA underside cleaning | 7 May, 1998

| We are about to use BGAs on our equipment. We clean all products prior to confomally coating them - to keep moisture off the IC legs. | Will this be a problem with BGAs. | Will we need to get the coating underneath the BGA or will the pitch on the balls be sufficient to prevent problems ? | Any comments appreciated. Cleaning under the BGA should not be a problem. Many of our customers, who still clean, use water wash equipment and have no issues with cleaning under a 1.27mm pitch BGA. As for requiring all of the leads (spheres) to be fully coated, that depends on your application. Typically if you have to coat leads on your .050" pitch leaded devices, then you'll also have to coat the spheres of the BGA. One problem you should be aware of is if you fill the gap between the BGA substrate, and the PCB surface, with the coating material, you could get broken solder joints in the field, if the board is subjected to any temperature extremes. The CTE of most coatings and potting materials is typically high ( >80ppm). The CTE of your board and solder joints will typically be 18-22ppm. We have seen cases were the coating fills the gap between the component and the board, then during temperature cycling the coating expands to the point of breaking the solder joints. If you would like to discuss this issue in greater detail, please call me at 512-933-5783, or the Motorola Customer Support group service line at 512-933-7289. Regards, Terry Burnette

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