NPL defect of the month

Manufacturing / Production Technology, Hardware & Services

Production/manufacturing equipment suppliers & service providers

13 October 2010 Manufacturing / Production Technology, Hardware & Services

October’s featured NPL defect covers cracking of the conformal coating as shown in the acoompanying figure, which was found after the circuit board assembly was returned from the field for investigation. This printed board assembly was in a medical application produced in a tin/lead assembly process in medium volume.

Some form of contamination under the mask had led to cracking on the coating. There was no evidence of corrosion or electrical failure on the sample board assembly. Large amounts of no-clean flux have been seen to cause lifting, not corrosion on boards. This is probably due to expansion and contraction of the material during thermal cycling. This movement of the material can lead to cracking of some brittle masks.

It would be necessary to review the board cleanliness and the coating compatibility with the intended application. Temperature cycling is probably the cause for the cracking but something under the mask must have caused it to expand and contract. If a mask is cracked it cannot provide suitable protection to the surface of the board. If a no-clean flux was the root cause the volume of material left on the surface of the board during assembly would need to be reviewed.

Dataweek’s latest featured NPL defect video, which covers the topic of ‘toe fillets’ encountered with QFP gullwing terminations, is available at www.dataweek.co.za/video.

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Manufacturing / Production Technology, Hardware & Services

NPL defect of the month

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