How many dimple need to be used for keypad metal dome?

metal_dome_5_dimplesLast article I mentioned that my company applied the metal dome without dimple as keypad contact solution just like the cell phone but we had trouble and met keypad press insensitive  issue. Now we solved the problem by adding the dimple back to the metal dome and still reach 1,000,000 (one millions) times of finger press cycle life.

We did some failure analysis and found the keypad insensitive defect was caused by two major issues.

  • One is the foreign contamination, include dust and fiber, that I mentioned at last article.
  • Another one is the oxidation show on the immersion gold finished surface on the ENIG board pads.

We found the oxidation particles look like the chemical of Phosphorus (P) exuded from base material of PCB. The P is one of the major element for the ENIG fabrication process. So we only can control less P but can’t remove it from the board.

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The Importance of Dimples in Metal Dome Keypads

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

Recently, our company introduced metal dome technology as a contact solution for rubber keypads, a trend also seen in many cell phone keypad designs. The advantages of using metal domes include a better key press experience, extended lifespan, and improved reliability. According to data, metal dome keypads can endure 2,000,000 finger presses compared to the 300,000 presses of poly-dome keypads. read more…》

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 Guideline for Flex cable(FPC) Trace Pattern

FPCMany FPCB designers may not be well-versed in the manufacturing process and its limitations. Workingbear have often come across designs that don’t meet DFx requirements, where designers insist on their approach, leading to numerous quality issues during mass production.

In an effort to prevent future quality failures and high costs due to yield losses, I propose that FPCB suppliers share some manufacturing insights regarding flex cable (FPCB) design capabilities.

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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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