Basic knowledge of FPC assembly

The flexible printed circuit board (FPC) process on Mount SMD in international miniaturization of electronic products, the surface is quite a part of consumer products mount, because the assembly space, the SMD is mounted on the FPC to complete the assembly of the.FPC on the SMD surface mount has become one of the trend of SMT technology. The technology requirements of surface mount and note the following points.


One:Conventional SMD mount


Features: mounting precision requirements are not high, the number of components less, component varieties to resistance capacitance based, or individual special-shaped components.

Key process: 1 Printing: FPC appearance by positioning in the special printing plate, generally use a small semi automatic printing machine, can also be used in manual printing, but manual printing quality is worse than semi automatic printing.


2 stickers: generally can be manually affixed, the location of high accuracy of individual components can also use manual placement machine placement.


3 welding: generally reflow welding process, special circumstances can also spot welding.


Two: High precision mounting


Features: FPC must be labeled with MARK substrate positioning, FPC itself to smooth.FPC fixed hard, mass production is difficult to ensure consistency, high requirements for equipment. In addition the printing solder paste and mounting process difficult to control.

Key process: 1.FPC: fixed from printed patch to reflow soldering process fixed on the supporting plate. The plate for thermal expansion coefficient smaller. There are two kinds of fixation methods, mounting accuracy of QFP lead spacing above 0.65MM by A method; mounting accuracy of QFP lead spacing below 0.65MM with B. method


Methods: A plate is sleeved in the positioning template.FPC with thin high temperature resistant adhesive tape fixed on the supporting plate, and then let the supporting plate and the positioning template separation, high temperature resistant adhesive tape should be printed. After reflow must be moderate viscosity, easy to peel, and no residual glue on the FPC.

Methods: B plate is a custom, the process must be after thermal shock times after deformation is minimal. T type splint is provided with a positioning pin, pin height was slightly higher than that of FPC point.


2: because the FPC printing plate loading, FPC is resistant to high temperature adhesive tape for positioning, the height and the supporting plane is not the same, so the printing must be selected. The elastic scraper has great influence on the composition of solder paste printing effect, must choose the appropriate paste. In addition to the use of B method for printing template after special treatment.


3:SMT equipment: first, printing machine, printing machine with the best optical positioning system, otherwise the welding quality will have a greater impact. Secondly, the FPC is fixed on the supporting plate, but the association between FPC and plate by tiny gap, which is the biggest difference with the PCB substrate. The device parameters of printing effect of placement accuracy, welding effect will be greatly affected. Therefore FPC mount of strict process control requirements.


 

(Source: Inside information)

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