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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

smt on flexible board

ron chua


smt on flexible board | 19 December, 1999

Hi, how to ensure flexible boards do not warp after reflow and still remain flat for subsequent operations. What is the best way to hold and transport these strips from one process to another. Thanks!

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Re: smt on flexible board | 20 December, 1999

Ron, The simplest way to process fexible PCB's that I have found is to use a process carrier fixture. There are companies that manufacture process carriers that are capable of holding flex through stencil, placement and reflow. The carriers are capable of providing registration pins and clamping mechanisms for holding the flex board in place. Carriers that are designed to accomodate reflow are usually made of Delmat or similar high temp material. I do not want to break the advertisement rule for the forum, but I know of two companies that manufacture such products. They are S.P. Manufacturing or MB Manufacturing. I hope this helps



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Re: smt on flexible board | 20 December, 1999

Ron: Chris is correct that there is a bunch of fixture fabricators that make good products that will serve your purpose. Other fixture fabricators can be found in the archives. Problems with these fixtures are:

1 Out-rageously expensive 2 Very long a fabrication lead time 3 Limited ability to use fixtures on multiple products

Consider making fixtures from unclad FR4. A local board fab can provide the laminate material. Sources for press-fit pins can be found in the archives.

Good luck

Dave F

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Re: smt on flexible board | 20 December, 1999

If your flex circuit is only populated on one side, you can have the PCB vendor palletize the flex for you. What you do is have the flex circuit laminated to 062" FR4 using a thermoset adhesive like Dupont WA. Standard flex circuit adhesive. However, the flex circuit is only laminated just beyond the border of the circuit. This leaves the flex circuit unbonded to the FR4 but the border areas permanently attached. So if your circuit is 1" X 1" your adhesive has a window 1.1" X 1.1". The flex circuit border can be pre blanked or unblanked. Population is just like a hard board. After population the flex circuit can be trimmed using a laser, exacto knife cutting only tabs connected to the flex border, or kiss cut using a steel rule die. I know this sounds like a lot of work but it allows the flex circuit to be processed like a normal hard board. I have build flex circuits many ways, with a permanently attached piece of FR4 used as a carrier, with a vacuum fixture, and taping flex boards to pallets. For high volume single sided flex, flex laminated to an FR4 carrier is the method I like.

Good luck,


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