This is true if you do not use a qualified material i.e. one that acts as a
heatsink. We manufacture many pallets for this very purpose and the material
we use is very insulative therefore it is a very pore heatsink and does not
alter the ability of the board to absorb heat. In the past people made
pallets out of aluminum and this of course was poor choice, but today
delmat, durostone, duralast and the like are suited quite well. in fact some
people have us design pallets with a pocketed bottom just to keep the bottom
side parts from reflowing again when they do the topside. Good designers are
familiar with the reflow environment and design accordingly. Of course no
one approach works for every situation.
Jim Gleason
Garland Service
972-494-1911
www.goGSC.com
-----Original Message-----
From: Edward Brunker <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Tuesday, January 19, 1999 11:35 AM
Subject: [TN] Re[2]: [TN] One more thing on Double side reflow
> Yes, nice idea! But how do you get maximum support on a complex
> assembly for the printer without it creating massive heat sinking
> scenarios which ruin the thermal characterisics of the assembly with
> regard to reflow.
> I believe the two are in opposition to each other. Printing requires
> large mass in the support with as much contact under the board to give
> adequate support. Reflow requires pallets which have as little contact
> with the assembly underside as possible, thereby NOT sinking heat from
> the upper side reflow.
> I have designed alot of jigs for such purposes, and don't agree with
> putting the two aspects together.
> Regards
>
> Edward Brunker
> Senior Process Engineer
>
>
>______________________________ Reply Separator
_________________________________
>Subject: Re: [TN] One more thing on Double side reflow
>Author: <[log in to unmask]> at INTERNET
>Date: 19/01/99 12:06
>
>
>Wade,
>
>Just a small point,
>
>If your are have to use a pallet - use it to the maximum benefit.
>
>Often you can (print) place and reflow both top side and bottom side in one
>hit(dependent on pad pitch).
>Think about the cost savings!
>No line changeover
>No Single side stock
>Easier product management
>One stencil
>One placement program
>Faster loading (2 times as fast)
>
>If you then extend this idea you can do 4,6 and 8 up.
>
>If you can get into bed with the pcb manufacturer you can also avoid post
>routing / break off.
>
>The carrier design especially board registration) becomes fairly critical
>but in Europe this is very popular, and is becoming more so in USA.
>
>A small picture of an 8 up can be seen on
>http://www.datumdynamics.com/smt.htm
>
>Please contact myself or Chris Chapman ([log in to unmask](401)
>683-5300) if you want any more info.
>
>Regards
>
>Fin
>
>Finlay Buchan
>Tel +44 (0)1290 426200
>Fax +44 (0)1290 426212
>Email [log in to unmask]
>
>
>Web Page http://www.datumdynamics.com
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Wade Oberle
>Sent: Monday, January 18, 1999 3:18 PM
>To: [log in to unmask]
>Subject: [TN] One more thing on Double side reflow
>
>
>Andrew,
> One more thing, we use the same alloy of solder paste on both
>sides of the board.
>
>There has been one board where we had to build heat resistant pallets to
>support the boards and keep the heat from side 1 when reflowing side2.
>This was due to the fact that we had many large mass components on both
>sides of the board. The pallets worked great but they cost $150 each
>and need periodic repair and are an obstruction to high volume
>manufacturing.
>
>Wade Oberle
>[log in to unmask]
>
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