Hi Jim -

Recommend that your fixture material be something of relatively low thermal
mass to minimize its affect on your processes.  Check into some of the
composites used for solder fixtures and tooling.  Stainless steel, unless it
is very thin, will act as a thief for the process heat.

Regards - Kelly


-----Original Message-----
From: Marsico, James <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Thursday, September 28, 2000 7:04 AM
Subject: [TN] DENSE ASSEMBLY (PART II)


>I want to thank those who responded to my request for suggestions regarding
>the assembly of my dense board.  If you recall, it is 6002 Duroid, .005"
>thick, 1.5" x 2", with 270 0402s on it.  The direction I'm leading to is to
>panelize the boards (6" x 9").  The panel will be placed on a solid plate
>(.050"?) and held in place with another plate (window frame) on top.  This
>would allow me to go through pick & place and reflow by handling the
fixture
>only.  How does this approach sound?  Would you suggest the fixture be made
>of stainless steel or should I consider a more thermally stable material
>like graphite?
>
>Second question...  This assembly is being used for a high frequency RF
>application, so solder coating the boards will effect performance.  (Just
>try and HASL this board!)  The RF guys like bare copper, gold, silver,
maybe
>even nickel or tin plating.  Does anyone have any recommendations regarding
>surface finish for this assembly?  (from a board fabrication and assembly
>process perspective... I'll deal with the RF guys).
>
>Thanks again,
>Jim M.
>
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