Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Screen Printing with a Pallet.



Screen Printing with a Pallet. | 12 July, 2001

I have a PCB that requires me to use a pallet for support. I was wondering if anyone out there is currently doing this. My biggest concern is screen printing. I think I know how to handle it - but just want to know about any pitfalls.

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Screen Printing with a Pallet. | 12 July, 2001

First, we don�t like pallets, but ya gotta do wat ya gotta do!!! Second, we used to pallet after print and before place, but we lost so many prints messing with palleting boards that we now pallet, print, place. Third, most of our pallets are �home brew� from laminate. Some times the laminate warps and we get bounce errors in printing and place. We like pallets / boards designed to do both top and bottom side.

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Screen Printing with a Pallet. | 12 July, 2001

A) Questions: 1) What sort of pallet materials used? 2) what PCB thickness & LxW size? 3) what stencil type & thickness used? 4) what profile type used (peak deg-C)? 5) any peak Deg-C contraints for the components SMT onto the PCB?

B) We use pallet support, for 0.8mm PCB placement onto pallet, screen print paste with pallet support, auto-send to SMT p&p process (with pallet support), and reflow using pallet support.... (reflow was RTS profile with peak 215 deg-C)

C) Suggested Pitfalls to detect : 1) pallet material plays part, coz selection materials can absorb Deg-C away from the PCB, you need to artificially increase De-C profile to accomodate this, and is usually (from our experience) evident and present by "De-C dips" in the profile different zones travels of the lonely singular PCB panel...

2) Ensure your pallet supplier can provide to you his permissible tol% for pallet thicknes variations... and control it, baby, control...materials selection of pallet must have stable predictable thermal expansion rates...go do the math (not you, the supplier...)

3) PCB thickness prone to warp? if thin, just tape down on four corners... if thick PCB, (never done thick PCB with pallet) try same?

That's all I can fit in for now, share any further findings with us, if you care to share.... (gosh that ryhmes!!!)

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