(3) Scribe and peel method of masking

In scribe and peel method, the masking material is required to have different characteristics compared to the other methods since the masking on the substrate is hand peeled. For the other methods, properties such as corrosion resistance, applicability, durability, adhesion strength are of the utmost importance. But for the scribe and peel method...
(1) Flexibility
(2) Surface adhesion strength
will need to be of proper mid values. This is shown in [Fig.1].

The combination of flexibility and adhesion strength is important. If the masking is not thick enough or not adhesive enough, it will peel off the surface and will cause increased side etching [Fig.1](a). If the masking is excessively thick or lacks flexibility, gas will collect beneath the masking and cause an over-hang [Fig.1](b). When the masking has the appropriate adhesion and flexibility properties, a well controlled milled cross section is obtained as can be seen in [Fig.1](c).

Masking material used for scribe and peel method can generally be categorized into Elastomers and Plastics. There is not a clear border line between the two and they even behave similarly under certain conditions. However, they differ that the elastomers are resistant to heat.
For non-oxidizing acid and alkali etchants, neoprene rubber, acrylonitrile rubber, and butyl rubber are used as maskants. For highly oxidizing etchants, polyvinyl chloride, polyurethane, butyl rubber are used. These masking materials are dissolved in solvents and evenly applied on work pieces. To apply, immersion, spray, pour, roller methods are used.

In order to achieve etched surface uniformity, the etchant concentration must be controlled, temperature fluctuations must be prevented to a minimum, and the work piece must be held in the etchant in a manner the gas does not remain on the surface. For that reason, various physical manipulation to the work piece is applied such as rotated, overturned, and rocked. Also, some chemical etchant additives such as anti-forming agent to prevent surface gas-outs, and surfactants to lower surface tension to ease gas relieving.