Photofabrication Engineering Inc.

Enabling New Technologies through Metal Etching Applications

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Design Guides

Click Here for a PDF of the PEI Design Guidelines for the Photochemical Machining of Ferrous and Non-Ferrous Alloys

Click Here for a PDF of the PEI Design Guidelines for the Photochemical Machining of Titanium


Design Guide for Photochemical Machining

When designing or specifying photo-etched/chemically machined parts, there are certain guidelines which will help expedite your project.

 

PEI presents this Design Guide to help generate prints which take the etching process into consideration. Data are given for a variety of metal thicknesses.  These data are generally applicable to the equipment, processes, metals and configurations.  They do not, however, define the ultimate capabilities of photochemical machining.

 

If your specifications do not agree with any part of this guide, please contact your PEI sales engineer for advice.

 

Due to the nature of the etching process and the inherent undercutting at the edges of the resist pattern on the surface, all dimensions, tolerances and configurations are a function of the part thickness, the material itself and, to a lesser extent, the process variables. 

In the sections which follow, data is given for a variety of metal thicknesses. This data is generally applicable to the equipment, processes, metals and configurations. They do not, however, define the ultimate capabilities of photochemical machining.

 

Dimensions & Tolerances

For dimensions such as slots, corners etc., there are a few guidelines for designers which express practical limitations when the dimensions under consideration approach the thickness of the metal. The most common rules are as follows:

 

Relationship of Hole Diameter & Features to Metal Thickness

Generally, the diameter of a hole (D) cannot be less than the metal thickness (T). This relationship however, varies as the metal thickness changes. A more exact relationship is illustrated below.


Metal Thickness (T)

0.001 in. - 0.005 in. (0.0254 mm - 0.127 mm)

0.005 in. (0.127 mm) or over

 

Smallest Hole Diameter (D)

0.004 in. (0.1016 mm)

At least 110% of the metal thickness

 

 

       

 

            

 

Some practical hole sizes attained from sample thicknesses are shown in below.

 

Metal Thickness (T)                    Hole Diameter (D)                                  Tolerance

0.0010 in. (0.0254 mm)              0.004 in. (0.1016 mm)                +/-0.0005 in. (0.0127 mm)

0.0050 in. (0.127 mm)                0.0060 in. (0.1524 mm)              +/-0.0010 in. (0.0254 mm)

0.0070 in. (0.1778 mm)              0.0080 in. (0.2032 mm)              +/-0.0015 in. (0.0381 mm)

0.0100 in. (0.254 mm)                0.0120 in. (0.3048 mm)              +/-0.0020 in. (0.0508 mm)

0.0200 in. (0.508 mm)                0.0240 in. (0.6096 mm)              +/-0.0030 in. (0.0762 mm)

 

Practical features such as length and width follow the same rules as holes. When in doubt, consider 1. 2 x T for dimensions and 0.15 x T for tolerance. Tighter tolerances can be achieved. Call the PEI Sales Department for more information.

 

Relationship of Line Width to Metal Thickness

The width of metal between holes is not a particular problem in chemical machining. However, when this space is the remaining surface area in a large field of slots or holes. there are limitations as to how small the metal width between the holes can be. This relationship is shown below.

 

Metal Thickness (T)                              Space Between Holes (W)

Less than 0.005 in. (0.127 mm)               .005 in. (0.127 mm) or over

At least the metal thickness                     At least 120% of the metal thickness

 

Relationship of Inside Corner Radius to Metal Thickness

The smallest corner radius is approximately equal to the thickness of the metal (i.e., for metal 0.002 in. (0.0508 mm) thick. the corner radius would be 0.002 in. (0.0508 mm». Under certain circumstances, this radius can be made smaller. Contact the PEI Sales Department when there are requirements for a radius smaller than the metal thickness.

 

Relationship of Outside Corner Radius to Metal Thickness

Outside corners tend to etch more sharply than inside corners. Therefore, radii less than the metal thickness can be obtained. As a general rule, outside radii are considered to be at least 75% of the metal thickness (T). At PEI, however, artwork can be created that will produce outside corner radii approaching zero, if required.

 

Relationship of Feather to Metal Thickness

Etchant attacks the material laterally as well as vertically. Assuming that the material is being etched equally from two sides, a bevel is produced. As a general rule, when etching from two sides, the feather (F) is approximately 10% of the metal thickness.

 

Center-to-Center Dimensions

Chemically machined parts will duplicate the center-to-center dimensions which exist on the production artwork.  Due to the nature of artwork preparation, there are some practical center-to-center dimension tolerances for finished parts, as shown below.

 

Center-to-Center Dimensions                                Tolerance

1.0 in. (25.4 mm) or less                                      +\-0.0005 in, (0.0127 mm)

1.0 in. - 3.0 in. (25.4 mm - 76.2 mm)                    +\-0.0010 in. (0.0254 mm)

3.0 in. - 6.0 in. (76.2 mm - 152.4 mm)                  +\-0.0020 in. (0.0508 mm)

6.0 in. - 10.0 in. (152.4 mm - 254.0 mm)              +\-0.0030 in. (0.0762 mm)

 

 

Metals

PEI has the capability to chemically machine the following materials:

 

Aluminum, Beryllium Copper, Brass, Bronze, Copper, Copper Alloys, Invar, Kovar, Magnesium, Mild Steel, Molybdenum, Nickel, Nickel Alloys, Nickel Iron, Pewter, Phosphor Bronze, , Silver, Spring Steels, Stainless Steels, Tin, Titanium, Zinc, Zirconium, Zircalloy, Zinc Alloys

 

Contact PEI’s Sales Department with your specific metal requirement

 

Thicknesses

Alloys with thicknesses of 0.005 in. (0.0127 mm) to 0.125 in. (3.175 mm) are chemically machined at PEI

 

Examples of Precision Parts and Decorative Keepsakes Produced by Photochemical Machining:

 

Advertising Premiums, Anodes, Aperture Strips, Anodes, Bearing Retainers, Bookmarks, Brackets, Business Cards, Bus Bars, Cams, Carrier Plates, Cathodes, Cavity Lids, Chip Carriers, Circuit Plates, Chopper Wheels, Christmas Ornaments, Contacts, Contact Arms, Clip Fingers, Covers, Diaphragms, Digital Read-Out Symbols, Die Cavities, Discs, Drive Bands, Dynode Grids, Electrical Connectors, Electric Shaver Heads, Electrodes, Electron Gun Grids, Electron Tube Grids, Electron Tube Shielding, Electronic Chassis, Elements, EMI Shielding, Encoder Discs, Extendible Antennas, Filter Elements, Filter Supports, Flat Springs, Flexures, Fluid Logic Components, Front Panels, Fuel Cell Anodes & Cathodes, Fuel Nozzles, Grids, Ground Springs, Heat Sinks, Heater Elements, I.D. Plates, Instrument Dials, Instrument Gears, Integrated Circuit Connectors, Iris Plates, Jewelry, Jewelry - Silver Plated, Jewelry - Gold Plated, Jewelry - All Finishes, Kotabs, Laminations, Lids, Light Choppers, Light Valves, Leadframes, Magnetic Recording Head Laminations, Magnetic Shielding, Masks, Medical Devices – External & Implantable, Medical Instrument, Probe Shields, Metal Scales, Metal Stencils, Microelectronic Masks, Micro Forceps, Microwave Components, Motabs, Motor Laminations, Name Plates, Ornaments, Pointers, Premiums, Pressure Sensing Diaphragms, Radar and RF Antennas Retainers, Retaining Rings, Reticles, Ribbon Shields, RF Shielding, Rotor Brushes, Rotor Switches, Screens - All Types, Shaft Encoders, Shaped Shims, Shims, Shutter Blades, Springs, Spring Clips, Step Lids, Strain Gauges, Strap Suspension Assemblies, Surgical Blades, Survival Blades, Switch Blades, Tape Cleaner Assemblies, Tear Bands, Thermal Planes, Thermal Switch Components, Timer Locks, Tooling Templates Translators, Washers, Wiper Contacts, Vacuum Masks

 


Design Guidelines for the Photochemical Machining of Titanium

When designing or specifying for photo-etched or chemically machined titanium parts, there are a few guideline adjustments required. These modifications become more dramatic as the part thickness requirement increases. PEI offers this Design Guideline addendum as a general instruction to help our customers produce prints which take the titanium etching process modifications into consideration. If your specifications do not agree with any part of this guide, contact your PEI sales engineer for advice. Because of the nature of the etching process and the inherent undercutting at the edges of the resist pattern on the surface, all dimensions, tolerances and configurations are a function of the thickness of the stock being etched, and to a lesser extent, the process variables. This data that follows does not define the ultimate capabilities of chemical machining but is intended to be a helpful resource.

Dimensions & Tolerances

For dimensions such as slots, corners, etc., there are a few guidelines for designers which express practical limitations when the dimensions under consideration approach the thickness of the metal. The most common rules are as follows:

Relationship of Hole Diameter & Features to Metal Thickness

Generally, the diameter of a hole (D) cannot be less than twice the metal thickness (T). This relationship however, varies as the metal thickness changes. A more exact relationship is illustrated below.

Metal Thickness (T) Smallest Hole Diameter (D)
0.001” - 0.006” 0.008” Ø
0.007” - 0.012” ≈ 1.2 x T
0.013” – 0.020” ≈ 1.4 x T
0.021” – 0.040” ≈ 1.6 x T
0.041” or over ≈ 1.8 x T

Features such as length and width follow similar rules as holes. Tighter tolerances can be achieved with advanced consultation. Call the PEI Sales Department for more information.

Relationship of Feature Spacing to Metal Thickness

The distance (or land) between holes or other openings is only problematic in the chemical machining of titanium when narrow. The minimum “land” for titanium should be 2 x T or greater. This is especially critical with thicker stock.


Relationship of Inside Corner Radius to Metal Thickness

The smallest inside corner radius is approximately equal to the thickness of the metal (i.e., for metal 0.002” thick, the sharpest corner radius would be 0.002”. This rule must be relaxed with thicker stock, as the inside radii decrease somewhat.

Relationship of Outside Corner Radius to Metal Thickness

Outside corners tend to etch more sharply than inside corners. Therefore, radii less than the metal thickness can be obtained. As a general rule, outside radii are considered to be at least 75% of the metal thickness (T). At PEI however, artwork can be created that will produce outside corner radii approaching zero, if required.

Relationship of Bevel to Metal Thickness

This is where titanium differs most from other metals. Etching solution or etchant attacks metal laterally as well as vertically. Assuming that the material is being etched equally from two sides, a bevel or “feather” is produced at all the edges. When etching titanium, the width of the feather increases with the thickness of the metal.

0.030” thick titanium leaves ≈ 0.010” feather
0.020” thick titanium leaves ≈ 0.007” feather
0.010” thick titanium leaves ≈ 0.005” feather, etc.

The photo shows a 0.010” feather on a 0.030” thick titanium part.

 

 

 

 

PEI • 500 Fortune Boulevard • Milford • MA • 01757

www.photofabrication.com • 1-508-478-3582 phone • 1-508-478-3582 fax

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