Many medical devices and applications require small metal components that demand very specific characteristics. These can include:

  • Ultra-high precision
  • Very thin material
  • Unique physical features
  • Unique surface textures
  • Identification features
  • Extreme consistency part-to-part
  • Ease of integration into the final device
  • Competitive cost

Fig. 1 – A patterned series of tapered holes in stainless steel for a filtration application. The holes are 150 micron in diameter on one side, and 35 micron diameter on the opposite side.
In addition, different medical applications require components made from a variety of different metals including stainless steel, copper, alloys, laminates, and clad materials. It is often a significant challenge to balance the combination of the above characteristics with the desired material, while still maintaining cost and production volume requirements.

Photochemical Etching Can Improve Production

While numerous manufacturing technologies exist to create precision metal components, one technology in particular offers the capability to incorporate all of these characteristics into one seamless manufacturing process. Photochemical etching, also referred to as photochemical machining or chemical milling, possesses the unique ability to meet all of the above demands when compared to other technologies such as stamping or laser machining. Photochemical etching also eliminates the need for certain post-processing, such as removal of burrs and thermal stresses, sharpening of blades, etc. The development of continuous “reel-to-reel” etching production has dramatically improved production capacity while reducing cost and improving consistency in quality.

Common examples of etched components are surgical blades, surgical needles and lancets, micro-separation filters, screens, implants, springs, electrical contacts, and many others. Parts can be manufactured in thicknesses as low as 0.025mm (0.001"), up to 0.500mm (.020").

Advancements in etching technology allow levels of precision, both in physical feature size and in dimensional tolerances, which were previously considered unachievable for volume-production components. Micron-level precision is common for many applications. (See Figure 1)

Typically, the precision of the location of a particular etched feature can be in the single-micron level, while the actual size limitations of features (for example, how small a hole can be) is dictated in part by the thickness of the material being etched. Essentially, the thinner the material, the smaller the individual features can be. A good ratio to work with is that a hole diameter can be as small as 0.8 of the thickness of the material.

How It Works

The etching process itself is straightforward. The base material (typically stainless steel, but many other materials can be etched) is cleaned, dried, and then coated with a special photoresist layer on both sides. The photoresist layer is then exposed using UV light and an ultra-precision glass photomask, leaving the desired shape and surface features of the component protected by the exposed photoresist. All unexposed portions of the material are then subsequently etched away in a highly controlled chemical bath, leaving the desired component as the finished result. Sounds simple, but it’s the level of process control and photomask tooling design that really bring out the advantages of etching technology.

Fig. 2 – Examples of the various hole shapes that can be produced using photochemical etching by varying the etching process on opposite sides of the material.
Because the material is processed from both sides, it is possible to utilize different photomask tools on either side to provide unique features and dimensions on different sides of the finished component. For example, a separation filter can have a conical or offset hole configuration allowing better filtration or ease of backflushing. (See Figure 2)

The smallest diameter of the hole dictates the maximum particle size that can pass through the filter, but the larger opening on the opposite side can improve the filter’s ability to trap a larger amount of material. In another example, a surgical blade or needle can have a varying texture on one side and an identifying mark (such as part number or company name) on the other. The process is so precise that the blade comes off the production line razor sharp with no need for additional grinding or sharpening. Partial-etch technology also allows the material to be very thin for functional areas while providing thicker, more robust material in zones where structural integrity is important, such as mounting.