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ENIG; Au < 0.5 um to avoid solder joint embrittlement

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SMTA-64387182

#88042

ENIG; Au < 0.5 um to avoid solder joint embrittlement | 2 June, 2022

We are designing a new PCB that will include a 0.4 mm WLCSP IC package. The OEM’s application-note for this package states ENIG; Au < 0.5 um to avoid solder joint embrittlement. Our PCB fabricator specifies the ENIG Au thickness to be 0.04um, with a range of 0.05um to 0.125um typical. If the Au thickness is 0.125um on some PCB’s, will this cause any placement/soldering/reliability issues for the 0.4 mm WLCSP?

Thanks, Joe

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DWL

#88048

ENIG; Au < 0.5 um to avoid solder joint embrittlement | 3 June, 2022

I don't recall thicknesses off the top of my head but brittleness becomes an issue more for gold plating then ENIG. .125 um should be fine. also, gold ain't cheap so its unlikely your PCB fab will get anywhere near the max tolerance.

On the other end of the spectrum, I've had issues with very thin ENIG gold plating after washing in DI water. My guess is if the gold is thin enough, washing encourages the Nickle to migrate through. As long as you aren't washing your boards before soldering, it should be fine.

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SMTA-64387182

#88055

ENIG; Au < 0.5 um to avoid solder joint embrittlement | 7 June, 2022

Understood,

Thanks, Joe

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SMTA-64387544

#88067

ENIG; Au < 0.5 um to avoid solder joint embrittlement | 8 June, 2022

Au thickness of 0.125 um should not cause solder joint embrittlement. Also, PCB fab should offer Au thickness range between 0.05-0.075 um for better process control and reliability. Higher Au thickness may suggest black pads leading to solder joints failure- a different failure mode other than gold embrittlement.

Hope this helps!

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