Technetters,
My $.02.
We use fine pitch parts and have a very dense board (12" x 15") and had
some solderability issues with HASL. We went to "immersion gold" and it
got a little better, but the solder looked grainy and dull. We have since
gone to OSP and are expecting more improvement. I have not received any
board yields yet, but from all the info/comments/recommendations I
received, I am expecting additional improvement.
DT
At 04:37 PM 2/19/98 EST, you wrote:
>Matthew,
>
> From my experience with "Flash Gold" boards, I would have less solder
>related defects than a HASL'ed board, especially concerning fine pitch, and I
>would attribute that to the resulting flatness of the pads.
>
> Printing is much more consistent (better gasketing of the stencil), and
>the solder volume on each pad is not subject to the variances that HASL can
>give you. The PCB's are not subjected to the kind of heat that HASL processes
>require, so another benefit is less PCB warping too...(that sure has been a
>topic lately!)
>
> I've seen it used on many different types of boards, from
motherboards to
>memory module boards, PCMCIA boards, Graphic Accelerator boards, you name
>it...and I'm sure if there were any issues with reliability they would have
>evidenced themselves long ago.
>
> From what I understand, the amount of gold that is used is so small
that
>it doesn't affect the solder joint to any real degree...that's why it's so
>inexpensive. One thing that I did notice though when I first starting
building
>gold plated boards, was that the surface mount joints tended not to be quite
>as "sparkly" as joints on a HASL'ed board. It's not real noticable mind you,
>one might only see the difference if you held both boards next to each other.
>One way that you can get the joints to look a little better is to use 2%
>silver in your paste...most solder paste vendors won't charge you extra for
>that either....if you buy enough paste from them that is.
>
> -Steve
Gregory-
>
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