SMT : Process points for mounting flexible circuit boards

PCB (Printed Circuit Board) is a printed circuit board, referred to as a hard board. FPC (Flexible Printed Circuit) is a flexible circuit board, also known as a flexible circuit board or a flexible circuit board, abbreviated as a flexible circuit board. The miniaturization of electronic products is an inevitable development trend. For the surface mount of a considerable part of consumer products, due to the assembly space, the SMD is mounted on the FPC to complete the assembly of the whole machine. FPC is used in calculators, mobile phones, and digital cameras. It has been widely used in digital products such as digital cameras and digital cameras. Surface mounting of SMD on FPC has become one of the development trends of SMT technology.

There are many differences between the process requirements of FPC surface SMT and traditional hard-board PCB SMT solutions. If you want to do FPC SMT process, the most important thing is positioning. Because the FPC board is not hard enough and soft, if you don't use a dedicated carrier board, it will not be able to complete the fixing and transmission, and it will not be able to complete the basic SMT processes such as printing, patching, and heating. The following is a detailed description of the process points of FPC pretreatment, fixing, printing, patching, reflow soldering, testing, inspection, and sub-boarding in FPC SMT production.

FPC pretreatment

The FPC board is relatively soft, and it is generally not vacuum packed when leaving the factory. It is easy to absorb moisture in the air during transportation and storage. It needs to be pre-baked before SMT is put into the line to force the moisture out slowly. Otherwise, under the high temperature impact of reflow soldering, the moisture absorbed by the FPC quickly vaporizes into water vapor to protrude from the FPC, which is easy to cause defects such as FPC delamination and blistering.

The pre-baking conditions are generally 80-100°C and 4-8 hours. In special cases, the temperature can be adjusted to 125°C or higher. , But need to shorten the baking time accordingly. Before baking, a sample test must be done first to determine whether the FPC can withstand the set baking temperature. You can also consult the FPC manufacturer for suitable baking conditions. When baking, FPC should not be stacked too much. 10-20PNL is more suitable. Some FPC manufacturers will put a piece of paper between each PNL for isolation. It is necessary to confirm whether the piece of paper for isolation can withstand the set baking. Temperature, if it is not necessary to remove the release paper, then bake it. The baked FPC should have no obvious discoloration, deformation, warping and other defects, and it can be put into line only after being qualified by IPQC sampling.