Photochemical milling cuts RFI screening cost

Paul Boughton

When a customer approached Photofabrication Services for a quote to produce RFI screening cans, the company found that changing the manufacturing process and specifying a RoHS-compliant finish enabled parts to be formed and spot-welding after plating, resulting in a substantial reduction in both cost and lead-time.

Photofabrication Services has the capability to manufacture virtually any component from sheet metal ranging from 0.05mm to 1.5mm in thickness. One class of components where chemical milling is often the preferred method of manufacture is RFI (radio frequency interference) screening cans for use on electronic products.

The majority of screening cans are manufactured from 0.25mm to 0.5mm thick metal.
One of these parts was to be spot-welded. The base metal was mild steel, which was initially to be hot tin dipped. However, this type of plating is not compliant with the RoHS (Restriction of the use of certain Hazardous Substances, 2002/95/EC) Directive. After considerable thought and discussion with the customer, Photofabrication proposed changing the plating from hot tin to dull nickel. The benefit of this was that the lead-time and cost of plating were reduced by virtue of the way the parts were etched in sheet form – using retaining tabs to hold the matrix of components together – and then dull nickel plated in the form of an etched sheet. Photofabrication could then form the parts using half-etched fold lines and fly presses. Through its experience with previous projects, Photofabrication has found that dull nickel is the only type of plating for which forming post-plating is successful when using hard tooling.

Finally, there remained the need to spot weld the RFI screening can. Spot welding is usually performed pre-plating, as there is a risk that the protective properties of the plating will be compromised if welding is carried out post-plating. However, with dull
nickel-plated mild steel, the spot welding process creates a nickel-iron alloy that offers improved corrosion resistance compared with mild steel. Because the environmental application was neither hostile nor external, the corrosion protection for the spot welded component was more than adequate.

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