BGA PAD SIZE

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   Hello Everyone, 

I'm a newbie here and I've already read a few forum post of the same topic but still couldn't get the answer I'm looking for.

I am currently working on a BGA footprint with .26mm nominal ball size and .5mm pitch.
Is my understand correct that when ball pitch is .5mm and below the padstack will always be Soldermask defined? And if it's Soldermask defined, then it will automatically be a Non-Collapsing type therefore should follow the pad oversize rule?

I understand that the main reason for the pad oversize is to be able to use via in pad due to the limitation of routing traces in the same layer as the pad. 

If everything above is correct, does anybody know if they would also be true for BGA footprints that are use for System In Package technology?

Because right now what I was taught for SMD BGA footprints/Non-collapsing is that instead of making the pad size larger we are following the calculation for Collapsing ball and making our pad size smaller. Instead of using .33mm pad size we would use .22mm pad size.

But doing this kind of contradict/invalidate the reasons why a BGA with .26mm nominal ball size and .5mm pitch should use SMD pads and follow pad size calculation for Non-Collapsing ball.

And another question I have is if a pad uses 0 soldermask expansion would it still be classified as soldermask defined?

I'd really appreciate any input you could share on this.

BR,
Flat.

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flatronics Members Profile Send Private Message Find Members Posts Add to Buddy List New User Joined: 28 Oct 2021 Status: Offline Points: 8	Post Options Post Reply Quote flatronics Report Post Thanks(0) Quote Reply Topic: BGA PAD SIZE Posted: 28 Oct 2021 at 8:30am
	Hello Everyone, I'm a newbie here and I've already read a few forum post of the same topic but still couldn't get the answer I'm looking for. I am currently working on a BGA footprint with .26mm nominal ball size and .5mm pitch. Is my understand correct that when ball pitch is .5mm and below the padstack will always be Soldermask defined? And if it's Soldermask defined, then it will automatically be a Non-Collapsing type therefore should follow the pad oversize rule? I understand that the main reason for the pad oversize is to be able to use via in pad due to the limitation of routing traces in the same layer as the pad. If everything above is correct, does anybody know if they would also be true for BGA footprints that are use for System In Package technology? Because right now what I was taught for SMD BGA footprints/Non-collapsing is that instead of making the pad size larger we are following the calculation for Collapsing ball and making our pad size smaller. Instead of using .33mm pad size we would use .22mm pad size. But doing this kind of contradict/invalidate the reasons why a BGA with .26mm nominal ball size and .5mm pitch should use SMD pads and follow pad size calculation for Non-Collapsing ball. And another question I have is if a pad uses 0 soldermask expansion would it still be classified as soldermask defined? I'd really appreciate any input you could share on this. BR, Flat.



Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 28 Oct 2021 at 8:40am
	You cannot dog bone fanout a 0.50 mm pitch BGA. You can escape the outer row, but the inner pad rows require Blind via fanout. The BGA pad should be larger than the ball size to produce an annular ring for the hole. You might even solder mask define the pad to help secure it to the prepreg to pass drop tests.
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