We have been building with flex circuits for nearly three years now, its an automotive product utilizing lead free paste, I will give you a few pointers.
1. Evaluate your supplier carefully, make sure you have some kind of stretch tolerance on the print before you start production. Flex circuits are not as repeatably manufactured as FR4. 2. Pallet design, use three locating pins or tensioners instead of two, if the circuit gets a corner bent during handling you will still have two locating pins. 3. Use a vacuum pull on you support plate in the screen printer, only pull vacuum on the waste area of the array so you dont bend the flex in a critical area. 4. Number and track the pallets, as time goes by the pallets tend to grow and you will have transfer problems, have a go-no go gage and check the pallets on a regular basis. 5. Make sure the fiducials will read in all of your process equipment, I had to upgrade the camera in my screen printer in order to get repeatability. 6. You might want to consider using a cover plate after paste print, when moving down the line the flex can come off the pallet if fast conveyor speeds are used, air gets underneath the flex and it acts just like a parachute. 7. If you are using gold plated pads you might want to consider storing the opened packages in a nitrogen cabinet. 8. If processing skip mark boards be sure your placement machines can identify them repeatably. 9. Check to make sure your reflow oven can handle the additional temperature, some of the older ovens cannot. 10. Have a log and record lot #'s in case a problem arises you can easily quarantine the suspected lot and detect if the supplier tries to send in another suspect lot. 11. I would keep the product on the same line if you have that luxury. 12. Have your supplier give you the packaging specification and review them that they cannot get damaged during packing, shipment and unpacking.
reply »