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How EMS fabricate a PCB Assembly?

How EMS (Electronic Manufacturing Services) fabricate a PCB (Printed Circuit Board) Assembly?

This article is writing for the people who still not yet really under what is the PCB Assembly. Because WorkingBear found there are many people just come to this EMS area and still not yet well understand what is SMT (Surface Mount Technology) and what is Wave Soldering.

The PCB Assembly is a very popular technology in modem industry.  For example, the cell phone, Tablet, Computer, Television, Remote toy car, etc. all have the PCB Assembly module  inside. The  invention of PCB Assembly technology is really help the electric products development trend to small size and multi-function.

So, how EMS fabricate a PCB Assembly? It is almost automatic production line now through SMT or wave soldering process to solder the electronic components on the board to instead of hand soldering by iron. Of course, you still can hand solder all electronic components on the board as manual by yourself but you must take high risk for the poor solderability quality and can’t do it mass production. Besides, the 0201 small chip are hard to be hand soldered on board and some of the package that design the soldering point under the package body can’t be hand soldered. For example BGA, QFN, LGA package.

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How to select a good actuator design for right angle connector?

Right angle connector or flip lock connectorAs my personal feeling that Right-angle FPC ZIF connector is really more easily to use than Drawer type of ZIF connector. Even right-angle connector is good but do you know how to select a good design of this kind of right angle connector?

Recently my company met lots of component broken troubles for the electrical connector call “right angle connector” or “flip lock connector” in manufacturing production line. We found almost the defect connector broke at the ACTUATOR portion while operators first time tried to lift it after SMT high temperature reflow process. I’m sure the connector works fine before reflow.

I did a study on the connector and found it was caused by the connector itself while through SMT high temperature reflow process as below two reasons:

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The benefit to use shielding clips to instead of shielding frame

SMT can clipFor almost of the frequency radio apparatus, the Printed Circuit board must design the shielding frame/can to prevent the EMI (Electromagnetic Disturbance Interference) effect. The regular design will apply one shielding frame to mount on PCB by solder and another shielding can to cover on the frame to isolate the RF.

That means there will be two press tools cost before implement this solution. Beside, the shielding frame must be mounted on the PCB by SMT process. It requires lower flatness specification to keep the solder joint well. Most of the shielding frame asks its flatness meet 0.12mm maximum. Some of the shielding frame even asks the flatness must lower than 0.10mm maximum. Because of current stencil thickness is around 0.10~0.127mm only. It brings more difficult to form the shielding frame and raise its cost.

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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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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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