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

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Bad wetting after reflow

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Bad wetting after reflow | 9 April, 2010


I produce two types of board. - 100% Thru Hole - 50% thru hole and 50% SMT

For the second, I have a bad wetting after the reflow on the top.

The pcb board have Au-Ni pad. I use a water soluble paste. I clean the board with a solution with water. Next i use a flux with 19mg of acid and 3.6% of solid content. I use SN100C.

I think it's due to the oxidation of the pad after the reflow or the oxidation due to water when i clean the board.

What do you think of that? Do you have seen the same problems?

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Bad wetting after reflow | 9 April, 2010

So for your SMT1/SMT2/PTH boards, you have poor solderability during SMT2. [Even if you have no SMT2 and only ST1/PTH, our answer is the same.] We assume this occurs on one board part number only.

We guess that your bare boards have insufficient gold to provide adequate solderability protection of the second side. Gold thickness below 3 thou is porous and would allow corrosion of the second side nickel during first side reflow. Verify this theory by making sections of the bare board and measuring the gold thickness.

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Bad wetting after reflow | 9 April, 2010

I think the oxidation on the pad happens easily but do not on Au plated pad.The reason may be caused by improper cleaning or Au plating thickness in plating process. But,before suspecting the pcb board, you need to check your process or used material first to verify the variation or improper. Thanks

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Bad wetting after reflow | 13 April, 2010

Ok, Thanks

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