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September 2000

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Subject:
From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 6 Sep 2000 13:40:40 EDT
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In a message dated 09/06/2000 11:43:51 AM Central Daylight Time,
[log in to unmask] writes:

> Thechneters,
>
>  I'd like to know if there are special design rules for the solder mask on
>  PCB.
>  Most of PCBs I have seen have pads surrended with a gap and solder mask.
>  In our case I have got a PCB with solder mask on the periphery of BGA pads
>  (to prevent bridging according to the customer).
>  It seems to me that the solder mask on the periphery of pads is not so
>  efficient as expected to prevent bridging and it seems to be also
>  responsible of the poor mechanical properties of the joint.
>  Does anybody have experience with this weird technique (solder mask on the
>  periphery of pads)?
>
>  Thanks in advance,
>
>
>  Walter Horaud

Hi Walter!

I believe you're referring to Solder mask defined pads vs. Non Solder mask
defined pads. You're right when you say that it reduces reliabilty of a BGA
solder joint. Go to:

http://extra.ivf.se/ngl/E-BGA/ChapterE2.htm

and you'll find an article that addresses that very issue. The article also
states that there maybe an occasion in which it is better to use a solder
mask defined pad on the PCB, that is if the BGA device has solder mask
defined pads to which the balls are attached.

-Steve Gregory-

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