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Date: 19/02/99 04:21
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Date: Fri, 19 Feb 1999 10:19:56 GMT
From: "Edward Brunker"<[log in to unmask]>
To: <[log in to unmask]>
Subject: Re[2]: [TN] Squeegee Speed
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>The factorinfluencing this effect is how stencil gaskets to the board and
>you may need to look as points such as : Board finish
>Regards
>Edward Hale
I find this aspect intersting. Resist height is always more than the
plated copper height. For all alternative finishes with LPI, in my
experience. The resist over traces leading to pads brings the resist
up even more. The dome on HASL boards will protrude above, but only
for a portion of the pad, the edges still remain lower.
Does anyone spec the resist height to be less than the pads?
So stencils rest on the resist leaving 10 - 30 microns of free space
underneath.
Regards
Edward Brunker
>Evenin' all!
>
> My question is this: My stencil printer operator has said that he
>has to
>wipe our 6-mil stencil each pass to get the paste in the 20-mill pitch
>aperatures for a QFP to release well. We are using Amtech NC-559 type 3
>paste with 89.5% metal. The paste is not old. I considered using type 4
>paste, which has a much finer powder in it. I was told by Amtech that this
>finer powder paste will pack more densly into the aperatures and I could get
>some bridging, unless I order a new stencil with aperature reductions. Our
>squeegee speed is 0.6 inches/s, or 15mm/s. Is this too slow? Amtech
>suggested that at this slow speed, the paste could be rising out of the
>aperature, as if someone pressed on a wet sponge and it rose back to its
>original shape. What is a good squeegee speed for 20 mil pitch parts?
>Thanks all!
>
>Ryan Jennens
>TelGen Corp.
>
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