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Faster dissolution of tin anode at the top of the electrolyte thins down and cut-off

We are using Acid Tin plating for plating Plating PCB as etch resist. we have noticed that the tin anode is getting dissolving in the reverse manner in our pattern plating machine TIN bath.

So for we all use to witness that this TIN anode is to get dissolve from the Bottom to TOP & After the usage the anode use to looks like SWORD. Top side of the anode use to be with thick & the bottom side use to be with very sharp edges.

But surprisingly, yesterday I also witnessed that the anode is dissolving from Top to Bottom. If you refer the photo graph the bottom side of the anode is as it is & where as at the top side the anode had became very sharp. Because of this problem the anode had lost its support in the anode hook & fallen down in the bag it self.

Kindly suggest probable causes and corrective measures.

K M M Abubacker
process engineer - Bangalore, Karnataka, India
October 16, 2009

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It sounds like too much of the anode is submerged in the solution. As long as the anode to cathode ratio is OK, I like to keep the top of the anode about three inches above the solution level. If the top 3" portion is not in solution it won't erode (or be reduced). Other things to check are the sulfuric acid and tin metal concentration in the bath. If the tin metal is too low and the sulfuric out of whack, it will cause uneven anode erosion. I would also inspect the anode bags and replace them if necessary.

Mark Baker
Fellow Plater - Syracuse, NY USA
October 20, 2009

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It is likely that there are stray currents that are causing some of the anodes to dissolve in this irregular way.

Possible causes are parts or pieces of anode on the bottom of the tank, and/or poor contact between the anode bar and the anode hook(s). Another possible cause is anode fines that fall off the anodes as a metallic powder. The anodes in an acid tin bath should be bagged to prevent this.

So, check you tank bottom. If there is nothing conductive on the bottom, clean and wire brush the anode bar. And, if you don't use anode bags, consider using them.

Lyle Kirman
consultant - Cleveland Heights, Ohio
October 22, 2009