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Mounting craft requirement and matters need pay attention for FPC

Mounting SMD craft requirement on the PFC(printed circuit board) in the development of electronic miniaturization,due to the reason of assembly space a considerable part of consumer products that SMD is mounted to the FPC to complete the assembly of whole machine.Its the trend of SMT technical development to mount SMD on the FPC. For SMT craft requirements we should pay attention to points of below.

1.Normal SMD mounting of FPC

Characteristic:less higher of mounting precision,less components,is mainly for resistance and capacitance or for individual profiled components.The key process:

A.Tin paste printing: FPC is oriented to the professional printing pallet,usually use small semi-automatic or manual printing machine,but the latter ones printing effect is worse than the former.

B.Mounting:Normally adopt manual mounting,and some individual profiled components can apply for this method too.

C.Soldering:Often use reflow soldering,can use spot-welding in special circumstances.

2.FPC high precision mounting 

Characteristic:FPC itself need to be flat and have basal plate to mark with MARK.Its difficult to fix FPC or ensure consistency in bulk production,so high and strict requirements for device.In addition,its hard to control tin paste printing and mounting craft.

Key process:

FPC fixing:fixing FPC in the pallet the whole process from printing mount to reflow soldering,so it require small thermal expansivity for the pallet.There are two kinds of fixing methods:  method a is used when mounting accuracy is above 0.65mm of QFP pin spacing, method b is used below 0.65mm.

Method a:pallet cover oriented template. The FPC is fixed on the pallet with thin heat-resistant tape, and then the pallet is separated from the positioning template for printing.High temperature resistant tape should have moderate viscosity,can be peeled easily after reflow welding,without residual adhesive on FPC.

Method b:Custom-made pallet must require minimum shape change after repeated thermal shock. There is T-shape alignment pin,which is a little higher than the height of FPC.

Tin paste printing: we have to choose flexible scraper during printing process as pallet is load by FPC which has heat-resistant tape to make different height compared with pallet.Tin paste component affect printing result greatly,so we have to choose suitable one.Moreover,special treatment is needed for printing template if we choose B method.

mounting device.First,its better that the printing machine with optical positioning system otherwise will affect soldering quality enormously.Second,FPC is fixed on the pallet, but it always produces tiny gap between both of them,which is the biggest difference compared with PCB.Thus, the device parameter setting has great influence on printing effect,mounting and welding precise.So it requires strict process control for mounting.