Why Burn/In(B/I) still cannot screen out the DDR soldering fail?

Recently we met a DDR memory BGA (Ball Grid Array) soldering fail issue. Actually the is HIP (Head-In-Pillow) that two balls under the BGA package. We sent a people to field to check how customer do the operation and found the product can’t be powered on. The interesting is the product will be powered on once use finger to press the DDR memory component.

How come this happen? Production line said these products had implemented the power on B/I (Burn/In) for 12 hours at 40°C. Why we still see this kind of BGA soldering defect in field?

Before answer this question, we must understand how the HIP defect happen. The HIP is a solder joint defect where the solder paste deposit wets the pad, but does not fully wets the ball. It is usually caused by the deformation of PCB resin and BGA substrate during reflow high temperature. The deformation make the solder paste on pad and ball on BGA separately while solder become liquid phase. Once the parts start cooling and the deformation will gradually back to normal condition but the liquid solder also back to solid and make two balls as HIP.

HIP is a serious reliability and quality issue and will definitely affect to brand credit. The typical board level test (ICT, FVT) are hard to be screened out this kind of HIP defect. So the HIP defect often skip the production quality system and be sent to end customer. Sooner or later this kind of defect will be returned for repair.

Why factory implement B/I and do 100% functional test still can’t screen out this kind of DDR soldering fail?

This is really a interesting problem. Below statement is from WorkingBear personal experience and may be not true.

Thinking about when the HIP will actually show the circuit open? I think most of the situation will show while the product be powered on and electronic component start to run a period then PCB and BGA start to increase its temperature.That means product will stay at lower temperature while turn off the power and the PCB and BGA deformation will be slightly. The Two balls will be fault contact. After turn on the product a period time, the product will become hot gradually due to e-components will product thermal engine. The deformation will become worse and open the contact between two balls and result in function fail.

Below WorkingBear list the reason why EMS (Electronics Manufacturing Service) can’t screen out the DDR BGA fail:

  • Products implement the B/I but didn’t turn on to do self diag. function test.
    WorkingBear often see this situation happen in the EMS that  only produce the PCB Assembly and without box build. The product be powered on always from lower temperature cooling condition then power off after finish the test.
  • Products implement B/I and power on but didn’t do any diag. to run DDR test.
    Some DDR soldering issue may not affect to the product power on. It must run to some memory address then show the error.
  • Products implement B/I and power on to do diag. test.
    Some DDR function test fail will be gone once re-power. It better to have program automatic record its error message during diag. test to help operator to check product has any error happen or not.

So, If products implement B/I but didn’t well design program to run diag. test and record the error message then HIP soldering issue may not be easily to screen out 100%.

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