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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Flex circuits

#29267

Flex circuits | 25 June, 2004

We are doing what I believe is unique from everyone else. We are using a .010 thick flex circuit board populated with the usual components, sot-23, caps, resistors,etc. It is mountd to a carrier plate with the edges taped down but I am having trouble with wrinkles in the infield. Are there any suggestions to follow to help me keep these as flat as possible? Will warming them up first and then pressing them help?

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#29300

Flex circuits | 28 June, 2004

Things to consider are: * Thermal expansion characteristics of you flex and your pallet should be better matched. We use G-10. * Placement of your two sided tape should be better, more uniformly distributed. We run strips the length of the flex that we space about 1/2" apart. [At least that's what we think our operators do. Sometimes with stuff like this they get creative ... anything that works AND saves a second of time is what they run with, yano?]

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Bryan Sherh

#29365

Flex circuits | 3 July, 2004

> Things to consider are: * Thermal expansion > characteristics of you flex and your pallet > should be better matched. We use G-10. * > Placement of your two sided tape should be > better, more uniformly distributed. We run strips > the length of the flex that we space about 1/2" > apart. [At least that's what we think our > operators do. Sometimes with stuff like this > they get creative ... anything that works AND > saves a second of time is what they run with, > yano?]

Hi,Can anybody upload one picture of your pallet?because I never saw such a process with pallet through the production line....I want to know whether the pallet will come along with the pcb through the reflow oven?and whether the pallet affects the profile of your PCB?or whether you heat the PCB and components only from topside in the oven?or have you some concerns on the CTE dismatch of top and bottom side? Thanks a lot. Bryan Sheh

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KEN

#29367

Flex circuits | 3 July, 2004

....not unique. But tough as hell!

I build flex assemblies for a major P&P equipment manufacturer. Some are pure flex, most are ridgid flex. And of course, why put fiducials on the boards to help the process (why God, why me?)

We use pallets and tape too. Universal theme here. There is no easy answer to this. Kapton likes to "move" with heat and water...follow good board dry storage practices.

My largest Kapton board is 23 X 18 inches, 2 mil thick!

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Bryan Sherh

#30473

Flex circuits | 10 September, 2004

Hi, can you easily remove your board from the pallet?without bending or damage the board? Bryan

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Rob

#30474

Flex circuits | 10 September, 2004

Hi John,

We use Spray mount adhesive on durastone pallets, then kapton tape on the egdes. We have produced upto 25K flexi PCB's a day with this method. The trick is to get just the right amount on the pallet, to maintain tackiness.

Cheers,

Rob.

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#30477

Flex circuits | 10 September, 2004

Rob: What brands of spray mount adhesive do you: * Prefer * Like * Dislike

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#30479

Flex circuits | 10 September, 2004

This is all very interesting. One obsticle I have to live with is I have an adhesive backing applied to the flex circuit before being placed on the pallet. Once gone through the reflow process the flex board goes through a couple of assembly stages and then the adhesive backing paper is removed and the circuit is then adhered to a metal cylinder. Applying the adhesive afterwards increases handling and risks are then involved.

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Rob

#30490

Flex circuits | 14 September, 2004

Hi Dave,

3M� Spray 75 Repositionable 500 ml was the last we used due to a bright spark in purchasing, but production didn't get on with it too well.

The only one that really gives us good consistant performance was the original 400ml Spraymount aerosol(RS part No. 268-1291 in the UK).

We tried other brands over the years, but none of them were up to it (either too sticky, not sticky enough, or left residue). If I was better at filing I could probably name & shame.

We used adhesive backers as well, but we added them on after the assembly and wash (then punched out the circuits from the panels).

Hope that helps,

Rob.

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