Why metal dome keypad must design dimple on it?

Keypad contact pad with fiber contaminationforeign dust contaminate inside metal dome and make contact fail.

Recently my company phased in the metal dome as rubber keypad contact solution. This metal dome solution had been implemented to many cell phone keypad solution also. Better key press feeling, longer life and good reliability is the benefit to use metal dome. As data show  the metal dome keypad can sustain 2,000,000 times of finger press verse 300,000 times of poly-dome.

In the beginning we removed the dimple from the metal dome in order to reach higher key press life. Because of the dimple will damage the contact pad the PCB and obtain verdigris from the copper layer base of PCB. The verdigris will finally disconnect the metal dome and contact pad of PCB and result in keypad malfunction.

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HotBar FPC Design Notices

Hot_bar_thermodeThe HotBar soldering is a kind of selective soldering solution where connect two pre-fluxed, solder coated parts by pulse heating element, call a “thermode”, with proper temperature to melt the solder and re-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.

The regular HotBar reflow process is to pre-print the solder paste on the PCB then go SMT reflow to make the solder on the PCB. After that then stick the FPC on the board and melt the solder again through thermode to connect the FPC on PC board. It may need to apply the flux on the solder since original flux had gone during high temperature of reflow oven.

In order to mount FPC on PCB, a thermal-conductor inside FPC to transfer heat from thermode to PCB to melt the printed solder on PCB is necessary.

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Design for Flex cable(FPC) Trace Pattern

FPCMany FPCB designer are not familiar with the manufacturer process and limitation.  I always found design does not meet DFx requirement and insist on their design and finally bring lot of quality issue after mass production.

Here I ask FPCB supplier provide  some of the design for the flex cable (FPCB)  manufacturing  ability and hope it will prevent future quality fail or cost high due to yield lose.

Basically I do think designer and FPC manufacturer shall make more communication to understand each other requirement and make FPCB lower cost and higher quality and yield rate. This shall be win-win.

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Screen-Printing on PET(PolyEthylene Terephthalate) notices

PTF_sampleThe PTF uses silk-screen to print the silver and carbon combination conductive inks on PET substitute to reach lower cost purpose as compare with FPC (Flexible Printing Circuit). Unfortunately, the screen-printing still has some ability limits. Especially that it has problem for fine trace width and fine space. This article will discuss screen-printing on PET limitation.

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

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What is PTF(Polymer Tick Film)? PTF introduction

PTF samplePolymer 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.

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