Photo chemical

Technical Specifications / Guidelines

At, Kristeel, R & D is a continuous effort. Through the effort of our team, we have evolved some design guidelines to assist our clients to produce accurate and reliable components. When you are designing for or specifying photoetched or chemically milled parts, there are certain guidelines which will help expedite the job. Kristeel – Shinwa presents this design guide as a general introduction to help you supply prints which take the etching process into consideration. It is suggested that, if you have any question that your specifications are not in accordance with any part of this guide, you can contact our customer support engineer for specific advice. Due to the nature of etching process and its under cut edges of resist pattern on surface, all dimensions tolerances and configurations are a function of the thickness of stock being etched as well as the material and to a lesser extent, the process variables

Tab Positioning

Necessity of providing Tabs for the component:

  • To prevent components becoming detached from the main sheet and being lost in the etching machine sump.

  • To prevent complex components getting entangled while stripping off the photo resist

  • Tabs are often drawn across the etch Bands. These are in triangular shape & apex pointing towards the components. After etching, the Apex should be etched to a width of one thickness , so that the components can easily be broken out from the retaining sheet. Figure 1 shows both Internal & external tabs (only for illustration,) Our process can provide either of the two Internal or External Tabs.

Relationship of hole diameter to metal thickness

The diameter of a hole can not be less than the metal thickness.

Relationship of Inside Corner Radius to Metal Thickness

The Diameter of a Hole cannot be Less than the Metal Thickness

The smallest corner of radius is approximately equal to the thickness of the metal i.e. for metal thickness of 0.05mm, corner radius would be 0.05mm

Relationship of Outside Corner Radius to Metal Thickness

Outside corners tend to etch more sharply than inside. Therefore a radius of less than metal thickness is obtainable. As a general rule outside radius is considered to be at least 75% of the metal thickness T.

Relationship of Line Width to Metal Thickness

The width of metal between the holes is not a problem in Photo fabrications but when this space is the remaining surface area in a large field of slots/holes then there are limitations as to how small the metal width between the holes can be.

Relationship of Bevel to Metal Thickness

An etchant attacks the material laterally as well as vertically Assuming that the material is being etched equally from two sides, it can be easily seen that a bevel is produced. As a general rule, when etching from two sides, the bevel is Approximately 10% of metal thickness as shown in figure.

Etched Dimensions

Because of the many parameters involved in determining etching Tolerances, it is not practical to give a definite rule, which will cover all circumstances. Some of the more common variables, which will affect the etching tolerances, are type and thickness of metal, size of production run and number of critical dimensions per piece. For purpose of establishing some general rule of thumb, a tolerance chart of metal thickness indicating the etched dimensions that are achievable for the said raw material thickness is mentioned below: -

0.05 0.15 0.25 0.50
Aluminum alloys ±0.02 ±0.03 ±0.04 ±0.08
Copper & it's Alloys ±0.01 ±0.015 ±0.025 ±0.05
Nickel ±0.01 ±0.015 ±0.025 ±0.05
Steel Alloys ±0.01 ±0.015 ±0.025 ±0.05
Stainless Steel ±0.01 ±0.023 ±0.038 ±0.075

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