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Assemby of flexible printed circuits

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FGH

#66350

Assemby of flexible printed circuits | 16 May, 2012

Hi Guys, I´m looking for information about processing smt components on flexible printed circuits (printing, SMD assembly,reflow soldering and laser cuting). These flexible circuits comes from a roll of 300 mm width. I found some information about roll-to-roll process, but i think this system is not suitable with populated components. Any help about this subjet will be very appreciated. Thanks.

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#66356

Assemby of flexible printed circuits | 16 May, 2012

Here's some notes from a Bob Willis presentation

Assembly of Flexible Circuits with Lead-Free Solder Alloy [Bob Willis leadfreesoldering.com] * Flexible Circuit Construction ** Base Material - 0.05mm Copper 18/18 um ESPANEX from Holders Technologies ** Liquid Solder Mask -MPR80 Amber - Nippon Steel ** Solder Finishes – *** Immersion Nickel/Gold - Aurotech, from Atotech *** Immersion Tin - Stannatech from Atotech *** Immersion Silver - Sterling from MacDermid *** OSP - Glicoat SMD P2 from Shikoku * Assembly Pallet for Flexible Circuit ** Thermal relief areas on the base of pallet to improve delta T during reflow. Also consider drain holes under the flex if using vapour phase for lead-free reflow. ** Modified flexible pallet with thicker recess in the areas of the circuits and solderability test strips. Drain holes for fluid are positioned under the flexible when using vapour phase reflow soldering. ** Fixed and sprung pallets location pins used for the flexible. Protrusion of pins above the circuit was approximately 0.010.” ** Circuits do lift on the edge of the tooling holes which does not cause a problem during assembly. This may be due to the copper being relieved around the hole causing the flex film to distort when clamped. * Printing of Lead-Free Solder Paste ** 0.006” (150um) stencil was recessed on the base of the foil to allow for any protrusion of the pallet clips. The stencil was recessed by 0.003.” ** Printing of lead-free solder paste with a 0.006” (150um) stencil. Two different aperture sizes were used on three different component footprints. Specific design rules used on the solderability wetting strips. Recesses were placed around pin protrusions from the pallet. * Rework of Flexible Circuits with Lead-Free ** Rework joints with hot air pencil ** Use flux prior to reflow ** Remove and replace components ** Set-point on tool 340-360*C ** Use lead-free wire to set-up air pencil distance from joints for reflow ** Removal of solder shorts with solder wick ** Shorts purposely added to SOIC16 leads for testing ** Set-point on iron 380*C ** No issues of delamination or pad lift on parts after two rework operations. Pad dimensions for the parts used could be reduced to improve use of the surface area but adhesion of the pads would be reduced. Modifications can be made, but only when this is really necessary.  

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FGH

#66357

Assemby of flexible printed circuits | 17 May, 2012

Many thanks davef

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#66360

Assemby of flexible printed circuits | 17 May, 2012

These notes are from ~2005-6. I remember pictures of the pallets and the reliefs on the stencil. Bob may still have his presentation online. Check his site.

Attachments:

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#66373

Assemby of flexible printed circuits | 18 May, 2012

Hi,

Since you're looking information about flexible printed circuits,a book entitled "Printed Circuit Boards R. S. Khandpur" could give you lot of information about flex circuits from Design, Fabrication, and Assembly Phase.

The book contains comprehensive single volume self-teaching guide to the art of printed circuit board design and fabrication -- covering the complete cycle of PCB creation, design, layout, fabrication, assembly, and testing.

You can read some info inside the book from Amazon at this link :

http://www.amazon.com/Printed-McGraw-Hill-Electronic-Engineering-ebook/dp/B000YAT1RO

Or you can read more on Google books at this link : http://books.google.com.ph/books?id=m8sJBIMtETgC&pg=PA452&dq=IPC-FA-251+Assembly+Guidelines+for+Single+and+Double+Sided+Flexible+Printed+Circuits&hl=tl&sa=X&ei=0BS3T7yiCML6mAW8pNDNCQ&ved=0CDQQ6AEwAA#v=onepage&q=IPC-FA-251%20Assembly%20Guidelines%20for%20Single%20and%20Double%20Sided%20Flexible%20Printed%20Circuits&f=false

For Industry Standards, IPC-FA-251 Assembly Guidelines for Single and Double Sided Flexible Printed Circuits provides you a more detailed explanation on this field.

You can also search and read articles from electronics companies or any EMS since they are expert on that field. Maybe you can visit Bittele electronics for PCB fabrications, Assembly, and other PCB related concerns.

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#66386

Assemby of flexible printed circuits | 21 May, 2012

Ask for board fiducials if you're running arrays. Global fids on the panel do not work well. One handy product we use on flex is "Tacsil". Works well on SMT pallets as well as router operation. It's double sticky stuff that helps hold on to the PCB's. Watch for delam if running rigid-flex. You might need a fillet of epoxy at the transition. Environmental control in SMT is important at printing stage. Humid or hot conditions lead to many problems with printing fine pitch, flex assemblies in array format.

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#66387

Assemby of flexible printed circuits | 21 May, 2012

Polymide is like a sponge and absorbs moisture much faster than rigid substrates. Pre-bake your substrate for 2-4 hours at 125C and perform your soldering within 1 shift thereafter or seal in moisture barrier bags.

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#66429

Assemby of flexible printed circuits | 22 May, 2012

If your washing them in-line, heavy silicon mesh works good in cages to keep them from flying around.

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#66437

Assemby of flexible printed circuits | 23 May, 2012

There is also a good reference book on flexible circuits from Joe Fjelstad.

http://flexiblecircuittechnology.com/flex4/

This book covers everything from creating the flex circuitry itself to the assembly of flex circuits.

Also, roll-to-roll assembly of flex circuits is definitely possible, although there can be some limitations. However, it can be cheaper and usually much more efficient. The up front equipment investment is usually more than most people want to deal with, so usually flex circuits are processed in panels. We currently do both panel and roll-to-roll flex circuits and whevever possible we try to do a project in continuous rolls.

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