Design for photochemical etching
The first step in photochemical etching is to design the part to be etched. This design must take into account several technical factors, including the thickness and type of material used, the level of precision required, and any post-processing required. It is important to work closely with an experienced etching supplier to ensure that the design is optimized for the photochemical etching process.
Material Selection and Size
The substrate material used in photochemical etching must be compatible with the chemical solution. Typically, photochemical etching uses metals such as stainless steel, copper, and brass, but non-standard metals can also be etched using specialized chemicals
Generally speaking, chemical etching works best with thin materials ranging from 0.01 mm to 2.5 mm in thickness, with a maximum sheet size of 1500 mm x 600 mm.
The thickness and size of the material will also affect the cost of the etching process, with thinner materials requiring shorter exposure times to the etchant. Depending on the design, thicker materials may require multiple etching steps or longer exposure times to achieve the desired pattern or design.
Feature Size and Precision
Chemical etching can produce features that are much smaller than traditional machining techniques. Dimensions as small as a few microns can be produced, with the minimum etched feature size being determined by the material thickness, which typically has a 1:1 ratio. The accuracy of any through-etched feature can be as low as ±10% of the material thickness or a minimum of ±0.025 mm.
For deep etched features, material thickness becomes less important. Surface features such as fluid channels can be etched to a depth of 0.025 mm, however, the width of any etch depth will increase at a 2:1 ratio. For example, a depth of 0.025 mm will have an etch width of 0.050 mm.
The complexity of the design is another factor that affects the feature size achievable with chemical etching. Simple designs with straight lines and curves can be etched with greater accuracy than complex designs with irregular shapes, patterns, and contours. The size of the part being etched will also affect the level of accuracy that can be achieved, with larger parts typically requiring larger minimum etch tolerances.
Etch "corners" and inner/outer corner radii
During the etching process, metal is not only etched downwards, but also to the side, creating a V-shaped "corner" around the cut. This effect is called "undercut".
Controlled undercuts can be used to produce a variety of profiles, providing products with unique characteristics, such as sharp cutting edges or tapered openings.
Etching sharp corners also affects the internal and external corner radii of the produced part, with the minimum internal corner radius being proportional to the material thickness. The minimum external corner radius is typically 75%.
Etched Tags or Tie-Offs
Etched tags, sometimes called tie-offs, are small protrusions or indentations left on a part after etching. Etched tags are used to hold a part in place during the etching process or to aid in post-etch processing steps such as part identification or assembly.
Depending on component size, design, or tolerance requirements, components can be produced without tags; however, they are often necessary when the required tolerance is less than 15% of the metal thickness.
