Case study for the mold-in insert screw boss broken

Case study for the mold-in insert screw boss broken

Last time WorkingBear mentioned the potential root causes to bring the screw boss crack after mold-in screw nut insert. Actually we received the complaint from the field then asked EMS and plastic supplier to double check their inventory and found about 1% of the screw boss cracked after mold-in screw nut insert before box build assembly. That means no extra force and screw driver give to these screw bosses and the crack happen just from its inner stress. The defect rate increase to 30% after screw in the plastic case together.

So, what make this happened? Workingbear had pointed out 4 potential root causes  to bring the screw boss crack for the mold-in nut screw insert process.

  • Using too much of the re-grind resin
  • No pre-heat on the screw Insert parts
  • The improper molding parameter
  • Design risk 

Since we had proved the boss crack really happened from plastic parts itself. We held these poor quality plastic parts and question the plastic supplier why crack happen? The interesting is that plastic supplier challenged me back that they didn’t change any parameter for this plastic parts and they really don’t know what happen and how come the screw boss crack now?

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Selectively increase solder paste volume solutions

Why need to partially increase the solder paste volume?

This is in order to meet current smaller and thinner electric component design, the stencil thickness is made as thin as possible to accurately control the tiny solder paste which print on the PCB.

Unfortunately, there is not only small component be placed on the board but also includes big components. So how can this big electronic SMD component get enough solder paste volume to mount on the board? The stencil thickness is too thin to provide more volume and stencil aperture also can’t be opened  too much over pad size. There shall be another solution to provide extra solder paste volume to this kind of big component and also for the DIP components will apply  PIH (Paste in Hole) process.

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PCB rework: Selective solder mask removal by laser

PCB rework: Selective solder mask removal by laserDid you ever met a trouble need to rework to remove the solder mask from the PCB?  If yes then how you did?

We usually remove the solder mask manually  by knife or hand grinding tool. But these kinds of rework always damaged and broke the traces on the PCB and result in high scrap rate for PCB or PCB Assembly.

Today WorkingBear will introduce you a new method to remove the solder mask by laser machine. It is high efficiency and high reliability. If the laser power select property  then it will only remove the solder mask and without damage copper under the solder mask.

Actually my company had never did this kind of PCB rework quite a long time. Unfortunately, new top manager ask to reduce the design phase and roll in the product to mass production from 9 months to 6 moths. Make design quickly will need to pay something. There are about 10K pcs of the PCB need to be reworked to remove the solder mask to improve the ESD issue.

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TQRDCE Performance Expectations and Review

This is an example that implement TRQDCE form for vendor survey.

TQRDCE Introduction:

TQRDCE ChecklistThe strategy of company for establishing and maintaining long-term working relationships is through creating and monitoring mutual performance expect ions and measurements. Performance metrics, constructive feedback, as well as prompt corrective action by the supplier and by customer are fundamental to achieving continuous process improvement.

In order to provide customer with the means to measure our suppliers, the TQRDCE (Technology, Quality, Responsiveness, Delivery, Cost, and Environmental) review was developed. It is imperative that supplier maintain a competitive advantage by providing materials of the highest quality and lowest total cost, with the best delivery, responsiveness and technology available. The TQRDCE Review is a tool for measuring and communicating a supplier’s performance and to aid company in determining their place in future business relationships.

This review is being provided two weeks in advance of our scheduled meeting with [SUPPLIER] on [DATE] at [LOCATION]. it should be shared with the appropriate personnel at [SUPPLIER] with a focus on the development objectives. it is company’s expectation that [SUPPLIER] come to the review with a written action plan that addresses all the development objectives listed on the review.

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Improve BGA solderability by partial increase solder paste volume

BGA_X-Ray_pictureHow to improve the BGA (Ball Grid Array) package solderability is always a big challenge for SMT (Surface Mount Technology) process. Especially for the fine pitch (ball pitch less than 0.8mm) BGA is more difficult to be soldered on the PCB. Besides, it’s soldering quality is also hard to be inspected since its solder hide under its body and sometimes even can’t be inspected by 2D X-Ray inspector. (5Dx or angle rotation X-Ray maybe ok to inspect BGA soldering quality but expensive)

As experience tell us that most of BGA solderability fail is caused by the HIP (Head-In-Pillow) soldering defect and over 90% of the HIP defect show on four corners of BGA package. Because of the diagonal distance is longest and greatest impact from board warpage and BGA deformation. There are many senior SMT engineer had done some experiments and prove that Increasing the solder paste volume on the pads under BGA can reduce the HIP defect risk.

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