Problems in nickel electroforming on stainless steel mandrel

Hi Marc. From your e-mail address I looked up what your company does, but only by doing that was I able to understand your posting. Sadly, I think most readers will find it impenetrable.

Maybe we can tell the readers that it's not that your electroformed nickel objects have "nickel microparticles" in or on them; rather that you are making large quantities of very tiny discrete nickel electroformed objects, 500 microns diameter x 3 microns thick, and that you have named those objects "nickel microparticles".

Even then I'm confused. In an ideal world where the stainless mandrel were more durable, what steps get repeated and what steps don't?

Regards,

A. Hello Marc, Have you considered, instead of acid etching the stainless foil prior to photoresist application, electrocleaning it, followed by a mild, non-etching, acid dip. This should be enough for adequate photoresist adhesion. Stainless steel is naturally passive and may not need any passivation after the resist is developed, or you can passivate it at this point, prior to electroforming.

A. Marc,
your query leaves many unanswered questions so we can only surmise what you are doing. I suspect you are doing some form of reel to reel electroforming and the thinness of the stainless steel is to allow the (stainless steel) mandrel to be easily taken over rollers etc. You also do not say why you can only use the mandrel a single time.
However, I surmise that you are coating your stainless steel with some form of photoresist and that the flexing of the stainless steel is resulting in the photoresist cracking or being damaged in some other way. Alternatively the stainless steel is being damaged by your process - maybe the bends are too tight or the line is not adequately aligned.
An important feature in using stainless steel as a mandrel for electroforming is to have it adequately passivated. Of course, we assume you have done a proper pretreatment for it! I would recommend a 10 minute dip in 10% sodium dichromate solution, if you are allowed to use it still. If not, try a potassium permanganate [on eBay or Amazon] solution; alternatively, try using an electrolytic passivate for about 20 seconds. A good passivation will help ensure your electroforms detach form the mandrel with minimum difficulty. Be aware that you may need to reprocess the stainless steel mandrel after every use.
Returning to the photoresist, or whatever you use to create the required shape of your electroform. I note that the electroform is only 3um thick, so your photoresist or imaging coating is probably less than 5um thick. Your imaging pattern (ie photoresist) must be applied to the stainless steel mandrel before any passivation takes place. There are numerous ones available, both wet and dry application and positive or negative imaging. I would suggest you use one that is flexible, yet hard, but not brittle. You may wish to use an electrophoretic coating, as the film thickness can be very easily controlled - if so, try contacting LVH Coatings Ltd in Coleshill, Birmingham, UK.
In any event, the more information you can supply, the more useful any answers will be!

A. Hi Lion. I think I understand your question, but if I am misunderstanding it, sorry.

Those rounded edges were not created by plating. Rather, the edges were abrasively rounded before plating, which is good design practice.

Luck & Regards,

A. Hi. We've moved your inquiry to a thread about nickel electroforming onto stainless steel mandrels.

Is that pic you sent what you are trying to accomplish?

I don't know exactly how to get those rounded edges but I do know that in almost all cases when electroforming, the situation is rather the opposite of electroplating: the surface touching the mandrel is the "good" side of the final object and the last plated surface is the "back" side.

Perhaps this part was made by electroforming, face down, onto a thick layer of epoxy which already contained that rounded profile? Could it be that the epoxy was radiation (UV) cured in a fashion that allowed a "feathered" curing?

Luck & Regards,