Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

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Through hole reliablility lead free

Views: 1744

Charles Stringer

#44487

Through hole reliablility lead free | 12 October, 2006

Hi We are experiencing different failure modes between leaded and lead free through hole assemblies. The boards are PTH. In the case of lead free boards we are seeing fracturing of the component legs much earlier than we do with leaded assemblies. Note these are NOT joint failures but fracturing of component legs. Has anybody else noticed a similar effect and how have they resolved it.

Thanks in advance

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AR

#44497

Through hole reliablility lead free | 13 October, 2006

Hi

Could you specify what you mean by fracturing component legs?

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Charles Stringer

#44533

Through hole reliablility lead free | 16 October, 2006

Yes of course. The leg of the component breaks between the top of the solder joint and the component body. We can induce the same failure mode with lead free joints but usually after 10x longer on vibration.

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#44534

Through hole reliablility lead free | 16 October, 2006

The wording in your second post re: lead vs. lead free behavior seems to contradict your first post, but I'll assume you mean that the lead free boards fail sooner during vib. testing.

My question is, if this is the case, are the parts that are failing rated for the process temps you're using on the lead free boards?

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Charles Stringer

#44542

Through hole reliablility lead free | 17 October, 2006

Apoligies Steve if I did not explain myself clearly. We have made the same design using the same RoHs compliant components (which I am assured by the suppliers are process temperature capable) with both lead and lead free solder. Without wishing to confuse matters further we have used an immersion Silver finish PCB on both builds, we have also evaluated other finishes but for a straight back to back test, we used immersion Silver. Both builds have been subjected to a random sweep vibration @ 6g. In the case of the PCA with lead bearing joints, the first failures are showing after 40 hours of vibration with the pins on a 4 leg bridge rectifier breaking between the top of the solder joint and the body of the device. In the case of a board assembled using lead free solder, the same device fails after typically 4 hours. My current theory is that due to the reduced ductility of the lead free solder, the vibration stress is being concentrated into the pin causing the early failure. Has anybody else out there seen similar problems?

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