iwannarc
Nov 06, 2005, 12:35 AM
Rather than hijack the making (conventional) printed circuit board thread, I decided to start this thread, not so much as an expert but as a learner, hoping to get hints from others who may have experience doing flex printed circuit boards themselves.
The inspiration for this came from discovering that flex circuits are expensive to have made commercially, and finding a scrap of information indicating that it is possible to be done much more cheaply DIY:
http://www-cdr.stanford.edu/~wil/documents/flexCirc_soldering_tutorial/Flex_circuit_Soldering_Tutorial.html
where the second paragraph states the following:
"Making flex-circuits on your own may not happen flawlessly on the first try, but if one is persistent and methodical it is a skill that can be mastered quite rapidly (see flex circuit fabrication tutorial)."
Unfortunately the writer hadn't gotten around to writing the flex circuit fabrication tutorial, and I was temporarily setback by this problem.
Recently I looked up other material by the author, and found, in his Ph. D. thesis, a section entitled "Sensor Construction" with nice illustrations about how it is done:
"Commercially available strain gage arrays (Measurements Group, EA-06-125MW-120) were bonded to single-sided custom-fabricated polyimide (DuPont Pyralux 1 oz. copper clad KaptonTM laminate) flex circuits. The
pattern was created using standard contact print photo-imaging techniques. The polyimide laminate was dip-coated with positive photoresist (Injectorall Electronics Corp.) and developed with diluted Sodium Hydroxide (NaOH). Electrical junctions between the flex circuit and strain gages were made using solder paste and 13 μm thick copper foil to maintain a thin sensor profile.The two halves were bonded together using acrylic pressure sensitive (film) adhesive (PSA) ...Through-thickness electrical connections (vias) were provided by crimping and soldering small (0.062 inch diameter) metallic eyelets (purchased from Keystone Electronics) on either side of the substrate.."
I have now obtained some copperclad Kapton sheets and 3M pressure sensitive adhesive from eBay, and managed to find the eyelets and a tool to affix them at Mouser Electronics, and am awaiting some plain Kapton from eBay as well...there are several adhesive transfer tapes that are available, (these are like conventional adhesive tapes but after pasting down on a surface, the tape can be peeled away, leaving the glue alone, which can be between 1 and 5 mil thick, so that another surface can be stuck over the adhesive. Several different varieties of tape are sold by 3M (typically having a 3-digit number that indicates the type of adhesive used in the tape, and can be quite expensive if not bought from eBay. Also instead of the Kapton brand of polyimide, other polyimide may be used. One problem is that sellers on eBay sometimes dont give the needed details about the kapton or adhesive they have ... the thickness of the adhesive, the kind of adhesive, etc. The adhesive I bought is 2 mil thick (1 mil would be better if I wanted my board to flex in use, but since I am not using it in this mode, I guess 2 mils is OK. )
I hope to try the toner transfer system that is discussed in the printed circuit board thread, and hope to buy a cheap new ($100 only!) 600 dpi Laser Printer from Dell, and perhaps a laminator (although with the very thin Kapton sheets I don't know how strong the adhesion will be. I know some laminators have less of a gap between the rollers, so I might have to look for one of those.
Hmmm...some of the Kapton film I received has silicone adhesive on one side of it which is heat proof...how do I get it off to apply the adhesive transfer tape? - or do I paste it on the other side and let the stickyness of the sticky side wear itself out?
The inspiration for this came from discovering that flex circuits are expensive to have made commercially, and finding a scrap of information indicating that it is possible to be done much more cheaply DIY:
http://www-cdr.stanford.edu/~wil/documents/flexCirc_soldering_tutorial/Flex_circuit_Soldering_Tutorial.html
where the second paragraph states the following:
"Making flex-circuits on your own may not happen flawlessly on the first try, but if one is persistent and methodical it is a skill that can be mastered quite rapidly (see flex circuit fabrication tutorial)."
Unfortunately the writer hadn't gotten around to writing the flex circuit fabrication tutorial, and I was temporarily setback by this problem.
Recently I looked up other material by the author, and found, in his Ph. D. thesis, a section entitled "Sensor Construction" with nice illustrations about how it is done:
"Commercially available strain gage arrays (Measurements Group, EA-06-125MW-120) were bonded to single-sided custom-fabricated polyimide (DuPont Pyralux 1 oz. copper clad KaptonTM laminate) flex circuits. The
pattern was created using standard contact print photo-imaging techniques. The polyimide laminate was dip-coated with positive photoresist (Injectorall Electronics Corp.) and developed with diluted Sodium Hydroxide (NaOH). Electrical junctions between the flex circuit and strain gages were made using solder paste and 13 μm thick copper foil to maintain a thin sensor profile.The two halves were bonded together using acrylic pressure sensitive (film) adhesive (PSA) ...Through-thickness electrical connections (vias) were provided by crimping and soldering small (0.062 inch diameter) metallic eyelets (purchased from Keystone Electronics) on either side of the substrate.."
I have now obtained some copperclad Kapton sheets and 3M pressure sensitive adhesive from eBay, and managed to find the eyelets and a tool to affix them at Mouser Electronics, and am awaiting some plain Kapton from eBay as well...there are several adhesive transfer tapes that are available, (these are like conventional adhesive tapes but after pasting down on a surface, the tape can be peeled away, leaving the glue alone, which can be between 1 and 5 mil thick, so that another surface can be stuck over the adhesive. Several different varieties of tape are sold by 3M (typically having a 3-digit number that indicates the type of adhesive used in the tape, and can be quite expensive if not bought from eBay. Also instead of the Kapton brand of polyimide, other polyimide may be used. One problem is that sellers on eBay sometimes dont give the needed details about the kapton or adhesive they have ... the thickness of the adhesive, the kind of adhesive, etc. The adhesive I bought is 2 mil thick (1 mil would be better if I wanted my board to flex in use, but since I am not using it in this mode, I guess 2 mils is OK. )
I hope to try the toner transfer system that is discussed in the printed circuit board thread, and hope to buy a cheap new ($100 only!) 600 dpi Laser Printer from Dell, and perhaps a laminator (although with the very thin Kapton sheets I don't know how strong the adhesion will be. I know some laminators have less of a gap between the rollers, so I might have to look for one of those.
Hmmm...some of the Kapton film I received has silicone adhesive on one side of it which is heat proof...how do I get it off to apply the adhesive transfer tape? - or do I paste it on the other side and let the stickyness of the sticky side wear itself out?