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January 1998

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Subject:
From:
Douglas H Bennett- Sales Engineer <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Wed, 21 Jan 1998 14:02:29 -0800
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text/plain (82 lines)
Steve,

I would say that you do want side 1 to reflow as it goes through the oven a
second time.  Depending on the paste you use, there are going to be
different metal types within the paste and you do not want parts of the
paste going to liquidus without all the paste going liquidus.  I think that
may sound a bit confusing, but essentially, either you keep the bottom side
below the plastic range or you want it to go all the way into the reflow
range - put simply: going halfway is bad.

Then you of course run into problems with components falling off.  That's
when you use the formula (as I am sure you know) using component mass and
pad surface area with surface tension of the paste at liquidus.  If the
math shows your parts will fall off then you need to get the glue going.

If I can help further, you can contact me directly.

Douglas Bennett
Sales Engineer
Heraeus Amersil, Inc.
770-623-5630 ext 4225
[log in to unmask]



At 03:40 PM 1/20/98 -0500, you wrote:
>All,
>
>We have a new board coming up that will be 6.3" x 9.3" with 30-40 fine pitch
>(20 mil) per side (mostly PQFP, couple TSSOP).  Board will be 6-8 layers,
>.062 thick,
>~400-500 total components, 2 compliant pin connectors.
>
>Can I ask any of you who are processing boards with similar density what
>your reflow process
>is?  Will I have problems with a straight 2-sided reflow process or should I
>look at
>fixturing to keep side 1 from reflowing when side 2 is reflowed?  We have a
>Conceptronics
>HVN-102 (7-zone) reflow oven.  We do not have glue-dispensing capability at
>this time.
>
>Next generation of this product will have equal number of BGA on both sides,
>what do
>I need to be concerned about other than the rework process?  Thanks for any
>inputs...
>
>Steve
>
>
>----
>Steve Schrader
>VP Manufacturing
>Patton Electronics Co.
>http://www.patton.com
>
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