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Solder Connection Environmental Screening

#6298

Solder Connection Environmental Screening | 23 August, 2000

Dr. Lee: In using environmental screening tests to assess solder joint reliability, what are the effects that make low temperature vibration effective in screening of poorly wetted solder connections? What temperature and vibration profile are effective for this purpose?

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Dr. Ning-Cheng Lee

#6299

Re: Solder Connection Environmental Screening | 23 August, 2000

I presume you are referring to vibration test with fixed frequency at room temperature. One procedure describing the detailed profile is in MIL-STD-883E, Method 2005.2 (12/31/96). The approximate profile can be described as 60Hz, 20-70g, and 96 hrs test duration.

The high g provided by vibration really challenges the strength of solder joints. Therefore, joints with poor wetting or excessive intermetallics all tend to fail under this condition.

You can alter the test temperature to further aggravate the test condition. A lower temperature often magnifies the mismatch in TCE. On the other hand, a higher temperature weakens the solder strength.

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#6300

Re: Solder Connection Environmental Screening | 24 August, 2000

It seems that sceening at -20�C and using a vibration profile similar to the one you mentioned does a good job of high-lighting defective solder connections on assembled boards, but not affecting good connections. Why is this happening?

In there a similar effect in indium / tin solder connections?

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Dr. Ning-Cheng Lee

#6301

Re: Solder Connection Environmental Screening | 24 August, 2000

Low temperature aggravates the mismatch in thermal expansion between solder and parts and between components and boards, therefore can induce earlier failure.

The low temperature screening test should not be as effective when used on soft solders such as high In content In/Sn solders, due to the better compliance of the soft solders.

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