Materials & Capabilities
The dimensional tolerances achievable through photochemical etching vary directly with material thickness, following predictable relationships that allow designers to accurately specify part dimensions based on the material gauge they select. Thin foils at the lower end of the thickness spectrum can hold exceptionally tight tolerances as precise as ±0.001 inches (±0.025mm), representing some of the finest precision available in any metal fabrication process. As material thickness increases, tolerances naturally expand, typically following the general guideline of approximately ±10% of the material thickness. Understanding this relationship between thickness and tolerance is essential for optimizing designs and selecting appropriate material gauges for specific applications.
This tolerance behavior reflects the fundamental physics of the chemical etching process rather than limitations in equipment precision or process control. The isotropic nature of chemical etching, where material dissolves equally in all directions, creates inherent relationships between the depth of material being removed and the lateral dimensions of features. Recognizing these relationships allows designers to work within the process capabilities rather than fighting against them, achieving optimal results through informed material and dimension selection.
At the thin end of the material thickness spectrum, from 0.001 to 0.005 inches (0.025 to 0.125mm), photochemical etching demonstrates its remarkable precision capabilities. These gossamer-thin foils, barely thicker than heavy paper in some cases, can be etched with tolerances as tight as ±0.001 inches on critical dimensions. This level of precision rivals the finest mechanical manufacturing processes while offering significant advantages in terms of burr-free edges, stress-free surfaces, and the ability to create complex geometries that would be impossible to stamp or machine in such delicate materials.
The exceptional tolerance control in thin materials stems from several factors. First, less total material must be removed to etch completely through the thickness, meaning shorter etching times and less opportunity for process variation to accumulate. Second, the undercut that occurs as a natural consequence of isotropic etching is proportionally smaller. When etching through 0.002 inch material from both sides, each side etches approximately 0.001 inch deep. With a typical etch factor of 2:1, this produces only 0.0005 inch of undercut from each edge, consuming just 0.001 inch total of feature width. This minimal undercut allows tight control over final dimensions.
Third, thin materials respond more quickly to etchant, allowing precise timing control. The etch process can be stopped with minimal delay once breakthrough occurs, preventing the excessive lateral etching that would occur if material continued dissolving after achieving the desired depth. Fourth, registration between top and bottom phototools, while important for all thicknesses, has proportionally less impact on thin materials where small misalignments represent a smaller percentage of the total dimension.
Applications leveraging these ultra-tight tolerances include precision shims where thickness control within one-thousandth of an inch is critical for maintaining assembly tolerances, microelectronic lead frames where conductor spacing and dimensions directly affect electrical performance, encoder discs where pattern accuracy determines measurement resolution, precision apertures and masks where opening size affects optical or x-ray beam characteristics, and filtration screens where pore size distribution must be tightly controlled to achieve specific particle retention.
As material thickness moves into the 0.010 to 0.020 inch range (0.25 to 0.5mm), a common thickness range for many commercial applications including contact springs, brackets, structural components, and electronic parts, tolerances typically expand to ±0.001 to ±0.002 inches. While still representing excellent precision by manufacturing standards, the tolerance relaxation compared to ultra-thin foils reflects the increased undercut that accompanies deeper etching.
For 0.010 inch material, each side etches approximately 0.005 inches deep before breakthrough. With a 2:1 etch factor, this produces roughly 0.0025 inches of undercut from each edge, consuming 0.005 inches total of the feature width. While this undercut is predictable and can be compensated for in the phototool artwork, the increased amount of lateral etching compared to thinner materials naturally leads to slightly looser tolerance control. Process variations in etchant temperature, concentration, spray pressure, or conveyor speed have proportionally larger effects on lateral dimensions when etching time is longer.
Despite these slightly relaxed tolerances compared to ultra-thin materials, mid-range thicknesses still offer precision that exceeds stamping for fine features and complex geometries, matches or exceeds laser cutting without thermal effects, and provides excellent repeatability part to part and lot to lot. The ±10% of thickness guideline provides a reliable planning number. For 0.010 inch material, expect ±0.001 inch tolerance; for 0.015 inch material, ±0.0015 inch; for 0.020 inch material, ±0.002 inch represents typical achievable accuracy.
At the upper end of the standard photochemical etching thickness range, from 0.030 to 0.060 inches (0.75 to 1.5mm), tolerances expand proportionally, typically ranging from ±0.003 to ±0.006 inches. These thicker gauges are used when structural rigidity, load-bearing capacity, or durability requirements dictate heavier material than thinner gauges can provide. Applications include structural brackets, mounting plates, heavy-duty heat sinks, and components subject to mechanical loads or requiring significant stiffness.
The tolerance expansion in thicker materials directly reflects the deeper etching required and the correspondingly larger undercut that develops. For 0.040 inch material, each side etches approximately 0.020 inches deep. With a 2:1 etch factor, this produces roughly 0.010 inch of undercut from each edge, consuming 0.020 inches of feature width. This substantial undercut requires significant compensation in the phototool artwork and makes dimensional control more challenging than with thinner materials.
Process timing becomes more critical with thicker materials. Longer etching times mean more opportunity for process variations to affect results. Etchant temperature variations of just a few degrees, concentration changes as metal dissolves into the solution, or spray pressure variations all have larger absolute effects on dimensions when etching time extends to many minutes rather than the brief cycles required for thin foils.
While overall part tolerances follow the thickness relationship, specific features may have different tolerance capabilities. Hole diameters, slot widths, and opening dimensions generally follow the ±10% guideline closely. Edge-to-edge dimensions across entire parts may accumulate slightly larger variations if phototools expand or contract with temperature or humidity changes. Registration between features on opposite sides of the sheet typically holds within ±0.002 to ±0.005 inches regardless of thickness, though this represents a larger percentage tolerance in thin materials than thick.
Feature size also influences tolerance, with larger features generally holding tighter percentage tolerances than very small features approaching the minimum size for the material thickness. A 1.000 inch hole in 0.020 inch material might hold ±0.001 inch, while a 0.020 inch hole in the same material might vary by ±0.002 inch due to the challenging nature of controlling very small features where undercut consumes a significant portion of the nominal dimension.
Designers can optimize tolerance performance by selecting the thinnest material that provides adequate strength and rigidity, specifying tolerances based on actual functional requirements rather than arbitrary precision, designing features larger than minimum size when possible, and understanding that tighter tolerances than the standard guidelines may require special processing, increased inspection, and higher costs. Working closely with the photochemical etching manufacturer during design helps identify opportunities to achieve required performance while optimizing manufacturability and cost.
The direct relationship between material thickness and achievable tolerances provides predictable, reliable design guidelines that enable engineers to confidently specify photochemically etched components knowing what precision to expect across the full range of usable material thicknesses.
4020 Jeffrey Blvd. | BUFFALO, NY 14219
P: (716) 821-9393 / (800) 875-1093
Website by Luminus
