Design Guide & Suitable Metals
In The News
Most metals are suitable for the etching process. The method of production and the chemical composition both have a bearing on the rate of processing, the overall finished size, tolerance and the appearance of the etched edges. Some alloyed materials do cause particular problems to the process e.g. a high carbon content contaminates the etching chemicals unless filtered out at the processing stage (refer to the rate of etch). Silicon causes particular problems with both the etching rate and adhesion of the photo resist to the surface of the material (refer to metal preparation). Metals that have an alloying content of Cobalt, Palladium or Titanium have to be given careful consideration. These three alloys especially can be major factors in preventing a successful etch. Alternative etching chemistry can be used to etch Titanium. However, as most commercial etching machines use Titanium for the metallic components within, successful Titanium etch equates to a wrecked machine. Precious metals can be successfully processed, but as special chemistry is required most commercial etching companies do not process these metal types unless the volume is high enough to warrant the special conditions. The majority of metal processed is cold rolled stock. However, sintered metals such as Molybdenum can be successfully processed. Pre-plated materials are generally not processed as the etch rate of the plating metal will differ from the base metal. This could consequently cause tolerance problems and cut back the plated finish to unacceptable levels. Consequently plated components are etched and post plated.
Of the metal used for the process is always purchased as photo etch rather than standard commercial grade. The metal is cold rolled, high precision, especially in relation to the tolerance of the thickness of gauge. It also has a superior surface finish to standard commercial grade material. Although there are slight variations between metal types, the general rule for thickness tolerance is ± 8% material thickness. It is very rare that precision strip deviates to this tolerance band and the normal deviation in the ‘as rolled condition’ is within ± 4% of metal thickness. Surface finish varies according to metal type and condition. However the surface finish is always superior to standard commercial grade material stock. The raw material for processing is received in three forms; flat sheets, coil and specific size cut blanks. Sheet material is typically confined to thicker gauge copper and brass (Including and above 0.4mm), aluminum and annealed stainless steel (0.6mm upwards). This material can be supplied with the surface polycoated to prevent surface damage during transport/handling. There are no specific problems with sheet material provided the suppliers handle it with care and it is stored in an appropriate manner prior to processing.
.0002 to .125 inch thick for most materials