Design & Engineering Considerations
Engineers new to photochemical etching often make predictable mistakes that can compromise manufacturability, inflate costs, or result in parts that don’t meet functional requirements. These errors typically stem from unfamiliarity with the unique characteristics of chemical etching or from attempting to apply design principles from other manufacturing processes like stamping, machining, or laser cutting without recognizing the fundamental differences in how photochemical etching works. Understanding these common pitfalls enables designers to avoid them, creating parts that leverage the process’s strengths while respecting its inherent characteristics.
The most frequent mistakes fall into several categories including dimensional and tolerance specifications that don’t account for process physics, material selection that creates unnecessary complications or missed opportunities, inadequate consideration of how parts will be used or processed after etching, and failure to communicate critical requirements clearly to the manufacturer. Recognizing and avoiding these errors accelerates the path from initial concept to successful production, reducing the iteration cycles and prototype revisions that consume time and budget.
Perhaps the single most common mistake involves failing to account for undercut, the lateral material removal that occurs beneath the photoresist mask as the etchant dissolves metal. Engineers unfamiliar with the isotropic nature of chemical etching may assume that features will etch straight down through the thickness with vertical walls, similar to how a punch creates a stamped hole or how a laser beam cuts. This misunderstanding leads to confusion when prototype parts arrive with dimensions that differ from the CAD file dimensions, not recognizing that the manufacturer has appropriately compensated for undercut to achieve the specified final dimensions.
A related error involves attempting to pre-compensate for undercut in the CAD file itself. Some engineers, learning that undercut occurs, calculate an adjustment and modify their design dimensions accordingly. When the manufacturer then applies standard compensation during phototool creation, double compensation occurs, producing parts that are dimensionally incorrect. The proper approach is to always specify final desired dimensions in drawings and CAD files, allowing the manufacturer to apply appropriate compensation based on material, thickness, and established process parameters.
Another undercut-related mistake is designing features that are too small relative to material thickness. Specifying holes significantly smaller than material thickness or webs narrower than the thickness guideline allows sets up manufacturing challenges where undercut may close small openings entirely or cause narrow features to etch away. Following the rule that minimum feature size should approximately equal material thickness avoids these problems.
Tolerance specification represents another frequent source of problems. Engineers sometimes specify tolerances tighter than photochemical etching can reliably achieve for the given material thickness, perhaps copying tolerance callouts from stamped or machined parts without recognizing that different processes have different capabilities. Requesting ±0.0005 inch tolerances on parts in 0.040 inch material, for example, exceeds what photochemical etching can deliver and may require alternative manufacturing methods or process modifications that substantially increase cost.
The opposite error involves specifying no tolerances at all, leaving the manufacturer uncertain about which dimensions are critical and which can float within normal process variation. Without clear tolerance callouts, manufacturers typically apply standard tolerances based on material thickness, which may be tighter than necessary for non-critical features or looser than required for critical dimensions, potentially leading to unnecessary rejections or functional problems.
Another tolerance mistake is applying uniform tight tolerances to all dimensions regardless of functional importance. A mounting hole that must align precisely with mating parts legitimately requires tight tolerance specification. The overall length of the part, with several inches of clearance on each end in its installed location, may function perfectly well with much looser tolerances. Over-specifying tolerances where they don’t functionally matter drives up inspection costs, may reduce manufacturing yield, and provides no performance benefit.
Engineers should also recognize that extremely tight tolerances may require special processing, increased inspection, and selective acceptance of only the tightest parts from each production lot, all of which increase unit costs. When functional requirements genuinely demand exceptional precision, this investment may be justified, but applying such tolerances unnecessarily wastes resources.
Material selection mistakes create various problems. Using thicker material than functionally necessary sacrifices the tighter tolerances and finer features possible with thin gauges, increases material costs, and extends processing time. If rigidity requirements can be met with 0.015 inch material, specifying 0.030 inch material doubles the tolerance range and minimum feature size without providing functional benefits.
Conversely, selecting material too thin to provide adequate strength or rigidity creates parts that bend, distort, or fail in service. The temptation to use the thinnest possible material for maximum precision and minimum cost must be balanced against structural requirements and handling considerations. Parts that survive manufacturing but fail during assembly or use represent costly mistakes.
Specifying inappropriate material tempers or conditions creates difficulties. Requesting full-hard spring temper material when the application involves post-etch forming with tight bend radii may result in cracking during bending. Specifying annealed material for springs that require specific force-deflection characteristics forces a post-etch heat treatment operation that adds cost and may cause dimensional distortion.
Engineers sometimes design parts without considering how they’ll be processed after etching. Specifying tight tolerances on dimensions that will change during subsequent forming operations wastes inspection effort on pre-form dimensions while ignoring the post-form dimensions that actually matter functionally. Parts designed for plating should account for the dimensional changes plating creates, particularly for holes, slots, or mating features where plating thickness affects fit.
Designs intended for bending should consider bend allowances, material stretch, and the locations where bends will occur. Placing precision holes or critical features too close to bend lines risks distortion. Failing to specify which surface should be on the outside or inside of bends can affect appearance or functionality if the surfaces have different finishes or characteristics.
For parts requiring assembly, inadequate attention to alignment features, registration holes, or mounting provisions creates assembly difficulties. Features that facilitate fixturing during welding, bonding, or fastening operations should be incorporated during the etching stage rather than added through secondary machining operations.
Failing to clearly communicate which dimensions are critical, what the parts will be used for, what environmental conditions they’ll face, or what quality standards apply leaves manufacturers guessing about priorities. A drawing that shows dozens of dimensions all with the same tight tolerance provides no guidance about which truly matter. Notes indicating the application, critical functions, or specific concerns help manufacturers optimize processes and focus quality control efforts appropriately.
Not providing complete information about required surface finishes, plating specifications, edge condition requirements, or cosmetic expectations can result in parts that meet dimensional specifications but fail to satisfy other requirements. Explicit callouts for finishes, platings, marking requirements, and packaging instructions ensure everyone shares the same understanding of what constitutes an acceptable part.
Perhaps the overarching mistake is designing in isolation without early engagement with the photochemical etching manufacturer. Consulting with the manufacturer during the design phase, before finalizing dimensions and specifications, allows identification of potential issues, optimization opportunities, and design improvements that enhance manufacturability, reduce cost, or improve performance. Manufacturers possess deep process knowledge and extensive experience with what works well and what creates problems. Leveraging this expertise through early collaboration produces better outcomes than finalizing designs independently then hoping they’ll manufacture successfully.
Avoiding these common mistakes requires understanding photochemical etching’s unique characteristics, applying appropriate design rules, specifying requirements clearly, and collaborating with manufacturers. This approach produces parts that manufacture reliably, meet functional requirements, and optimize the balance of performance, quality, and cost.
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