FPC (Flexible Printed Circuit) also known as soft printed circuit board, flex pcb, referred to as flexible pcb. FPC is made of polyimide or polyester film as a substrate with highly reliable flexible printed circuit board.

FPC has a broad market, attractive prospects and high technological content, and is a rising industry. The equipment and process method for flexible printed circuit board surface assembly are basically the same as SMT. Because the flexible printed circuit board is thin and soft, the surface assembly soldering process is different from the rigid printed board in the following two points. First, the assembly and welding of the surface of the flexible pcb board requires the use of a carrier plate fixture (carrier) to convert it into a rigid pcb for solder paste printing, mounting, reflow welding, inspection and other processes. When processing, placing, transporting and cleaning the board, try to avoid excessive bending to prevent damage.

Difficulty of assembling SMD on FPC

(1) Fixed

SMD mouting on FPC, one of the key is FPC fixation. The quality of the fixation will directly affect the mounting quality.

(2) Selection and printing of solder paste

(3) Since the carrier plate fixture is made by machining, there is a certain degree of machining error between each carrier plate fixture.Therefore, it is required that the printing machine be equipped with an optical positioning system and use heat-resistant tape. In the SMT processing process that uses heat-resistant tape to bond the fixed FPC, the corners of the FPC have high-temperature-resistant tape for positioning, which makes the height of the surface inconsistent with the plane of the carrier fixture. Must use elastic rubber scraper. It is recommended to use high quality no-clean solder paste.

(4) Mounting components

Generally, multiple FPCs are placed on each carrier board fixture, and each FPC is fixed on the carrier board fixture.There will always be some small gaps between the FPC and the carrier board fixture. There will also be some machining errors between plate fixtures. Therefore, Mark is required to be designed on each FPC. When it is found that the mounting accuracy exceeds the standard, the Mark of each FPC can be treated as a "local Mark". Before mounting each FPC, take a picture of the "local mark" to ensure Loading accuracy.

(5) Reflow welding

When the FPC is well fixed, it can be said that more than 70% of the defects are caused by improper reflow welding process parameter settings. When reflow soldering, set the ideal temperature curve according to the material, size, and SMD of the FPC, especially the heat absorption of the carrier board, solder paste characteristics, and equipment conditions. Unqualified rate control within ten parts per million

(6) Cleaning

The cleaning method is similar to that of rigid boards, such as water-based ultrasonic cleaning, organic solution cleaning, etc. When FPC is cleaned after welding, a tray should be used to prevent damage to the assembled FPC.

(7) During the transportation process, a special tray should be used when picking, placing, and transferring the FPC. And try to avoid excessive bending to prevent damage to the FPC. In addition, in order to ensure assembly quality, it is best to dry the FPC before printing solder paste and mounting.