The potential cause for HSC peel off defect

Recently we found many missed segment defect for the HSC (Heat Seal Connector) solution LCM. As experience tell me the reliability of HSC bonding  process is not good for the industrial product. It is easily to miss-contact between the PCB and HSC after a period of use.

I only know the result but I didn’t know why in the past. In order to understand why the HSC bonding force is not good and trial to fix this kind of defect, I collect some information from expert and supplier and study the root cause.

PTF(Polymer Tick Film) process introduction

Polymer Thick Film (PTF) flexible circuits are manufactured by screen-printing conductive ink onto flexible substrates such as PET (Polyethylene terephthalate). It can be single layer or multi-layers circuit by further screen-printing dielectric materials as insulating layer and applying through-hole technologies.

• PTF: Polymer Thick Film (The article in Wikipedia)
• PET: Polyethylene terephthalate (The article in Wikipedia)

 

Notices for Screen-Printing on PET (PolyEthylene Terephthalate)

The PTF uses silkscreen to print the silver and carbon combination conductive inks on PET substitute to reach low cost purpose as compare with FPC. Unfortunately, the screen-printing has some ability limits. Especially for small trace width and small space.

• PTF: Polymer Thick Film
• PET: Polyethylene Terephthalate
• FPC: Flexibility Printing Circuit

Hot-Bar Flex cable Design Notices

The Hot-Bar reflow is a selective soldering process where connect two pre-fluxed, solder coated parts by heating element, call a thermode, with proper temperature to melt the solder.

Applying a pressure and contacting on the soldering target is necessary to melt the solder and insure that components stay in place during cooling.

Flex cable(FPC) Trace Pattern Layout Design Notices

Many FPCB designer are not familiar with the manufacturer and bring lot of quality issue after mass production. Here I summary some of the design notices for the flex cable (FPCB)  manufacturing  ability to prevent future quality fail.