As to problem of title, I have received the problem report from quality assurance department.

I would like to inform about problem report detail.

  • Problem detail
    Product ; ASTG12LVCC
    Quantity ; 42 units
    Problem contents :
    As to same site, error 99 was occurred at 42 units. Error was fixed by changing PCB and thermistor.
  • Analysis result.
    1)Analysis was carried out about sample thermistor (6 units).
    Analysis was carried out by SEMITEC limited(Thermistor’s manufacture company).

    * Resistor measure
    Resistor issue have found at 2 samples. , resistor value of another sample thermistor were no problem.

No.

 Resistor value(at R55 condition)

1

14.728

2

14.460

3

14.332

4

14.285

5

14.516

6

14.337
Regulation

13.629 to 14.472

  • * Disassemble and inspect about sample units which has resistor value error
    There is not electrolytic peeling and element portion’s issue.

    * Analysis of adhesion material
    As to sample No.1, they did not find the issue which will impact for thermistor’s characteristic.
    However, as to sample No.5, they found the adhesion material of metal.

    * Qualitative analysis of adhesion material
    Cu(copper) constituent was detected. therefore, they can think that electrode electric terminal element had been educed.



    * They guess that;
    Water is trespassed for inside of thermistor.
    then, conjugation of Cr-Cu interface became to lose.
    As the result, resistor value of thermistor became increase.

    2)About water’s pathway of entry for thermistor chip.
    * Simulation test
    (1) Comparison between sample unit and new one.
    Boil cycle test(100 cycle) there is not difference of result.
    PTC testing (2 atmospheric pressure, 120h) there is not difference of result.

    (2) Thermal shock testing (80 degree /5min normal temperature/30 sec 20 degree/5 min)
    by 2 kind tubes structure which is covered copper pipe of thermistor.


    As the result, in tube straight condition, all units become OK until 500 cycle(5/5).
    However, in tube 180 degree twist condition, 2 units become NG at 50 cycle(2/5)

    * They checked the presence or absence of transformation when thermistor attach to product. however, it was not specification which is subjected to extreme stress.

    3) Check appearance of sample units
    In sample unit, there were units that attaching surface between shrinkage tube and PVC tube was peeled off.
    • Speculation of this result’s cause.
      They guess that;
      *There was water intrusion at inside of thermistor. Then, resistor value had increased. As the result, product did misjudgement to error 99.
      *Some sample unit’s resistor value has returned to correct value by did evaporation of water of inside.
      *As to water intrusion, it can guess structure problem. The purpose of shrinkage tube installation was waterproof also.
      However, surely adhesion did not been carried out. because, it is small adhesion area, and adhering for soft material.
    • Measure
      PVC tube covers the copper tube. And, the size of shrinkage tube increases from 10 mm to 15mm or more.


      *Thermal shock testing had carried out by using counter-measure parts(by 500 cycle), then, there is no problem.
      *As to the specification covering PVC tube, there is no problem at manufacture.
      *Attach check also carried out, then, there is no problem.
    • Measure to product
      Already installed product; ; Measures by each location if problem is occur.
      As to spare parts stock(9900563011), it will replace to counter-measure parts.
      Stock product; no measures.
      Manufacture product ; it will measured from January 2015.