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ENIG Thickness for Flex

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RHK

#58576

ENIG Thickness for Flex | 13 April, 2009

We had an issue with the finish, PCB manufacturer is telling that they had a problem with the Nickel rework, which resulted in 20% fall out. Please help me by providing the ENIG thickness for Flex boards, is it same as rigid boards as per IPC 4552. I read in some papers that the PCB manufacturer will reduce the thickness of ENIG for flex or else the copper will be brittle and will result in cracks or fractures. Is there a spec for ENIG thickness for flex.

Any idea about High Phosphorous ENIG finish-this is just for information. Thank you in advance.

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#58583

ENIG Thickness for Flex | 13 April, 2009

Use IPC-4552 for your ENIG thickness.

Typically, ENIG has nickel deposit with medium [7-9 percent by weight] phosphorus content. That's what fabs do on rigid boards. On a flex with medium-P and IPC-4552 specified ENIG, you could see brittleness and cracking issues with the nickel. * If you reduce the thickness of nickel on flex to overcome brittleness issue, you open yourself to "black pad" failures. So, you're kind of blanked. * Work-around is to use high-P [10-13 percent phosphorus by weight] nickel to increase the ductility of the nickel.

This high-P nickel seems to limit gold thickness to 0.05�m, which is not the end of the world. But it's nice to know just how much gold is actually on the flex. Thickness measurements in this range are a bit dicey to perform, because of limited equipment accuracy [~+/- 0.01�m on a good day].

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RHK

#58604

ENIG Thickness for Flex | 15 April, 2009

Thank you! I am looking into this, but main idea is to use rigid board in place of flex.

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