Hole Size and Metal Thickness
Generally, the diameter of a hole should not be less than the thickness of the metal; however, this relationship does vary as the metal thickness changes.

TABLE 1    Metal Thickness to Hole Size

Metal Thickness (t) Less than .001" .001" - .005" .005" or over

Smallest Hole Diameter (D) Must be determined by test run At least metal thickness At least metal thickness

Line Width and Metal ThicknessIn most cases, the width between the holes is up to you. However, if you need to design a large field of slots or holes, please note the following guidelines:

TABLE 2    Metal Thickness to Hole Spacing

Line Widths

If the width of the metal at the surface is important, we need you to specify this on your print. An allowance will be made for the tab, which will be different. For example, a wire which measures .016" wide may only have a 010'' surface width due to the cusp/bevel factor (please see below).

Inside Corners and Metal Thickness
The smallest corner radius should be directly proportional to the thickness of the metal. For example, for metal thickness of .002", the corner radius should be .002"; however, if you need a smaller radius, it may be possible. Please call us at 1-800-875-1093, or email us, for clarification.

Outside Corners and Metal Thickness
Outside corners tend to etch more sharply than inside corners. Therefore, radii of less than metal thickness are possible. As a guideline, outside radii should be at least 75% metal thickness.

Corner Radii
Our photo-chemical machining process tends to round off corners. This is more pronounced on thicker material.  The advantages are:

• Higher quality parts, free of scratches or cuts.
• Improved production throughout in your operations because your parts don't catch on other parts

If you need a square corner, Precision Photo-Fab has techniques to accomplish this as well. For a sharp corner, simple changes to CAD designs can be incorporated!

Cusp or Bevel and Metal Thickness
Etchants attack materials laterally as well as vertically. This results in a condition for a hole known as a cusp or a bevel. The relationship of a cusp or a bevel to metal thickness depends on one-sided or two-sided etching.

If designing for one-sided etching:
If thickness=t, and cusp/bevel=A, A should = .4t
If designing for two-sided etching:
If thickness=t, and cusp/bevel=A, A should = .2t

The cusp (or bevel) is more pronounced in heavier materials. The cusp (or bevel) can be controlled through our process or can, in most cases, be eliminated by a secondary operation.

Tie-Ins or Tabs
Parts can be manufactured & shipped in one of three ways…

	Tabbed in sheet form – Parts are "tabbed" (connected) much like a model airplane kit.  Tabs can be either recessed or protruding, depending on your edge finish requirements.  Tie-ins (or tabs) can save you money by minimizing handling, therefore reducing manufacturing costs.
	Broken out - If parts are manufactured "tabbed" in sheet form, they can be "broken out" in-house prior to shipping. Note, this picture depicts "protruding" tabs on the left, top, and bottom of the part. The right side of the part shows two "recessed" areas where the tabs were removed.
	Etched clean - Acid etches entirely around the perimeter of the part.  This eliminates the possibility of burrs from tab removal.

Unsupported Tabs or Wires
We recomment avoiding unsupported tabs or wires.

Why?

Tabs can cause distortion problems in processing or handling, and they may sag or bend. When in doubt, call us and we'll help!

Etched Dimensions
There are no absolute design rules for etching tolerances.

The good news is our process can often provide the best solution for your needs.

As a general guideline, a tolerance of +/- 10% of the metal thickness is usually acceptable.

Metals
Most ferrous and non-ferrous metals, as well as a variety of other materials, can be etched by Precision Photo-Fab Inc.

The following list represents the most commonly etched metals.

Metals

Aluminum Brass Copper Beryllium-Copper Nickel Nickel Silver Nickel Chrome

Phosphorous-Bronze Carbon Steel Stainless Steel - 300 Series, 400 series Spring Steel (Coated or Uncoated) Numerous alloy combinations of the above metals Zinc, Monel, and PH15-7, PH17-7

Alloys

Alloy 42

Kovar

If you would like to work with us on determining the best material for you application, we would be glad to do so. Please don't hesitate to call us at 1-800-875-1093, or shoot us an email!