Handy Facts About Photochemical Etching

Metal Thickness Drives Everything

Minimum feature sizes, dimensional tolerances and costs are directly affected by metal thickness.

• Minimum holes or slot dimension is 110% of metal thickness
• Minimum ligature or land area is, generally, not less than metal thickness
• Minimum dimensional tolerance is +/-15% of thickness, to a practical minimum of +/-.0015" on metals .010" and less.
• Minimum radius dimensions are not less than 70% of metal thickness
• Etching speed is .001" -.002" per minute, depending on the alloy, and thus determines the total etching time.

Here's a link for additional information.

What Popular Metals Can Be Etched by Ferric Chloride?

• Carbon, Spring, Stainless and Silicon Steels
• Nickel, Nickel-Iron (Including Kovar, but not Havar), and Nickel-Copper
• Copper, Brass, Bronze (phosphor and Muntz)
• Aluminum (not anodized), Tin, Manganese, Zinc, Chromium, Indium
• Some "Super Alloys"
  • Inconel 600 and X750
  • Hastelloy X, A214

You can find more detail here.

What Metals Will Not Etch in Fe3Cl?

• Gold, Platinum, Palladium, Silver*
• Titanium, Tungsten, Tantalum
• Niobium, Zirconium
• Cobalt, Molybdenum*

* Conard has an alternative etchant for silver and moly.

How are Photo Etching Costs Determined?

Photo etching costs are about the "real estate": how many parts can fit on a sheet.  The size of the sheet is, to a large degree, determined by the dimensional tolerances. Part designs that accommodate standard drawing block tolerances of +/-.005"  on three-place decimals for metals up to .032" thick allow using the largest sheet size, often up to 18" x 24".

The "sheet" is the primary unit of labor, regardless of its size. Every sheet is handled into and out of each of ten sequential operations. The goal is to maximize the number of parts processed at each step, thereby reducing the labor per part.

The other significant cost variable is metal thickness.  Thicker materials take longer to etch, which is the most expensive part of the process.

 This chart illustrates the relationship between tolerances and costs.

How much do holes cost?

The first hole is always included in the price of the part.  Any additional holes, no matter how many are FREE. Always.

Is photochemical machining a Nadcap special process?

No.  Etching does not alter the mechanical or chemical properties of metal, therefore it does not qualify as a special process.  However, chemical milling can be used to alter metal characteristics and in some cases may be subject to Nadcap checklist 7108/5 criteria.

What will my parts cost to be photo etched?