Its hard to believe 32 years ago I populated my first SMT Flex circuit, using Serial#2 Pick and Place machine in the world, and produced the first ABS break circuits for Texas Insuments.
Back in the day, SMT Flex was chosen due to the Coefficient of Thermal Expansion. Dry lay-up Capacitor layers generated micro cracks with forces making flexible circuits the perfect medium for long life. This recent picture of a 32-year-old flex passed 1,000 Thermal shocks from -55C to 125C. With a 10 second transition. Not bad even by today’s standards
SMT Flex: Polyimide
Polyimide has always been the standard for SMT Flex. The polyimide film is successfully used in applications from -269C to 400C. With Polyimide, also known as Dupont™ Kapton® is the go-to film for all SMT flex applications. This film makes flex easy to manufacture in sheet or roll form, easy for SMT assembly, and easy for rework. Most contract manufacturers should be capable of manufacturing on Polyimide films with standard SMT equipment and reflow equipment. Reflow ovens designed for PCB manufacturing used for flex with modifications. High volume air flow and thermal stability with low mass flex is always a concern. Many film choices are available other than Polyimide for cost savings, or volume requirements.
SMT Flex: Dimensional Stability
This is where the fun begins! Flexible Circuits can move up to .001″/Inch and meet IPC Standards. If your assembly is 1.00″x 1.00″, it is easy to keep the components on the pads with all sizes, because the copper layer is only .001″x.001″ out of true tolerance. All component sizes 1206, 0805, 0603 to 01005 hit the pads. However, what if your assembly is 18″x 18″? Now the pads are out of tolerance by .018″x.018″. If you are placing 1206, 0805, 0603 to 01005 1206, 0805, and 0603 could float back into tolerance, but the 0402, 0201 and smaller will not even hit the pad. The tricks of the trade will allow for highly successful assemblies with even smaller components and other unique films.
SMT FLEX: Solder Paste
SMT Flex in sheet form does require fixture or tooling plate to maintain an even surface for printing solder paste. In most cases, SMT Flex is similar to PCB for printing. Locate the fiducial mark, align and print. Perfect every time. Well, almost. The acrylic adhesive system in Flexible Circuits and the solder mask used outgas. In some cases, it is no problem. In other cases, the outgas will oxidize the solder sphere causing unwanted solder balling. With a PCB, solder balls are invisible under components because the PCB itself is not transparent. With Flex, every solder sphere can be seen, because it is easy to see through the base material.
SMT Flex: Digital Graphics
High-resolution digital graphics are available with SMT Flex. For customers that combine flex in advertising, the back side of the flexible circuit manufactured with UV ink sets that achieve a 5-year outdoor rating. Standard CMYK+Spot Color is standard. 600DPI x 600DPI is available to transform graphics into flex.
SMT Flex: Lamination
For Roll-To-Roll (R2R) applications, lamination of PSA, Vinyl, Paper, Tyvac, etc. is standard. Layers are laminated after the SMT Flex is populated to achieve the final form, fit and function of the flexible circuit.
SMT Flex: Die Cutting
Many forms of die cutting are available on flexible circuits. Hard Tooling, Rule Die, Co2 Laser, UV Laser are standard offerings. Die cutting is available in Sheet form and high volume Roll-to-Roll manufacturing. Optically registered to targets giving good to best cutline accuracy.
SMT: Roll-To-Roll (R2R)
Roll-To-Roll manufacturing is for high volume customers. Minimum orders are one roll of Flex Circuits. Credit card sizes would yield 100K circuits per one roll. We have many Roll-To-Roll lines offering different solutions. Processing Polyimide, PEN, and Polyester films are standard. We also manufacture Paper, Vinyl, or other specialty films. High-speed robotics, XY gantry, and custom automation are standard. High volume contract Automated Assembly is our business.
SMT Micro Assembly
We are proud to be the first high volume Roll-2-Roll (R2R) micro assembly manufacture in the world. We manufacture from wafer to Roll-To-Roll flex. Please contact firstname.lastname@example.org for information on this proprietary process.