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Facilitating innovation in medical product design

05 July 2015

In the medical device sector, the key market drivers are an ability to produce efficient and ever smaller devices that are cost-effective to produce, and that can be manufactured in volume and to strict time-to-market parameters. Albert Tsang reports.

The photochemical etching process allowed for the etching of all 130,000 holes simultaneously in this blood micro filter

Demand for minimally invasive curative and diagnostic procedures is growing exponentially as patients and medical service delivery organisations seek to reduce operation and recovery times, and increase the accuracy of diagnosis.

Because of this, over the last decade, medical product manufacturers have been designing (and seeking to manufacture) smaller and smaller components with more and more complex and minute features.

Couple this with the overarching demand from patients and healthcare providers to rationalise the costs associated with medical treatment, and medical device OEMs are constantly on the lookout for cost-effective and efficient manufacturing processes. 

Where metal parts and components are concerned, increasing numbers of medical device OEMs are embracing the use of photo-etching as the manufacturing process of choice. Photo-etching is a versatile and increasingly sophisticated metal machining technology that can be used to mass manufacture complex and feature-rich metal parts and components.

Coupled with the fact that photo-etching uses easily re-iterated and low-cost digital tooling, it provides a cost-effective, highly accurate, and speedy manufacturing alternative to traditional machining technologies such as metal stamping, pressing, CNC punching, and laser and water-jet cutting.

Traditional machining technologies can produce less than perfect effects in metal at the cut line, often deforming the material being worked, and leaving burrs, heat-affected zones, and recast layers. In addition, they struggle to meet the detail resolution required in the smaller, more complex, and more precise metal parts that medical device OEMs require.

There are instances — typically when an application requires multiple millions of parts and absolute precision is not a priority — when these traditional processes may be the most cost-effective. However, if OEMs require runs up to a few million, and precision is key, then photo-etching with its lower tooling costs is often by far the most economic and accurate process available.

Another factor to consider in process selection is the thickness of the material to be worked. Traditional processes tend to struggle when applied to the working of thin metals, stamping and punching being inappropriate in many instances, and laser and water cutting causing disproportionate and unacceptable degrees of heat distortion and material shredding respectively. While photo-etching can be used on a variety of metal thicknesses, one key attribute is that it can also work on ultra-thin sheet metal, even as low as 10 micron foil.

Precision Micro has pushed the boundaries of what is possible with photo-etching, making advances in etchant chemistry and developing the process to embrace more and more metals. Numerous medical device OEMs have partnered with the company in the manufacture of often complex and safety critical products.

Micro filters are a good example. The nature of the photo-etching process lends itself to the manufacture of precise, reliable, and cost effective meshes and filters, many designs of which are impossible to manufacture using conventional machining or metal cutting technologies.

Moreover, lead times are reduced dramatically, as are contingent costs, as tooling set up and iterations (which are often necessary) are quick and relatively simple. Being digital, the tooling for photochemical etching can be manipulated on screen with ease and take a matter of hours rather than the days or weeks that would be expected with traditional processes.

Using the photo-etching process, Precision Micro can incorporate etched meshes up to 1,500mm by 600mm and in a wide range of materials. Varying bar sizes and open area ratios can be incorporated to control flow rates across the mesh, and - something that appeals to medical device design engineers - the photochemical etching process allows for far greater open areas than is possible using alternative processing technologies due to its ability to produce tiny and intricate wire sizes.

When compared with meshes that are woven, the single-part meshes and grids that are produced via photo-etching are characterised by their consistent cross-sectional thickness and accuracy of aperture shapes and sizes. Also, as they are manufactured from a single piece of metal, they are slimmer, have greater integrity, are robust when being handled, and the exhibit better electrical properties with no risk of poor contacts at the weave intersect.

One particular medical device OEM, working on a blood filtration product, had been frustrated in its attempts to produce a blood micro filter using various technologies and service providers.

Before coming to Precision Micro, the company had made the filter using a hugely expensive, time-consuming, and — due to the production of burrs on the underside of the component — inefficient and ineffective laser fabrication process.

Precision Micro’s job was to pierce a 78mm diameter, 50micron thick stainless steel disc with over 130,000 apertures, each being 100 microns in diameter on a staggered pitch of 200 microns with a maximum allowable tolerance of ±10 microns against a standard tolerance for photochemical etching of ±25 microns. 

As the photochemical etching process (unlike the previously used laser process) allowed for the etching of all 130,000 holes simultaneously, Precision Micro was able to provide burr and stress free filters and also produce the filter in a fraction of the time, providing the OEM with a cost-effective route to mass production.

Precision Micro has developed its own dielectric coating process for the inside of shielding cans for pacemakers, where the possibility of arcing exists between circuitry and the grounded shielding can. Arcing can occur as a result of turn-on spikes or surges (electromagnetic pulses) caused by external stimuli, and can obviously be very damaging to such electronic medical devices. 

For one particular large multi-national medical device OEM specialising in cardiac rhythm management, Precision Micro’s dielectric coating process was applied to the small screening can that sits in a pacemaker to stop EMI/RFI interference. It is possible for the insulating coating to be applied selectively to inside surfaces of the shielding can considered most susceptible to arcing, enabling cans to be designed to fit in with reduced profile requirements favoured increasingly by electronics designers.

Branded ‘MicroSafe’, this exceptionally even coating is pinhole free and has no detrimental effect on the shielding efficiency of the formed can. Adhesion to the substrate metal (usually nickel silver) is excellent, and the upper operational temperature is claimed to be in excess of 260°C.

In another application, the key attributes of photo-etching — namely its ability to produce parts in high volumes that are burr and stress free — made it an ideal choice for the manufacture of flat springs required for a hearing aid assembly. For this application, material performance and integrity was critical.

The diaphragm needed to flex absolutely precisely over and over again, and so competing machining processes such as stamping, pressing, and punching — which induce either compressive, tensile, or sheer stresses in the metal being processed — struggled to produce consistent quality parts.

In addition, the extremely thin nature of the springs — ranging as they do from 38-100 microns — coupled with their small overall size (4mm x 8mm), introduced other manufacturing challenges. It was vital that these parts exhibited clean profiles, which was achievable through the photo-etching process, and parts that were burr free. For mass production of these parts, photo-etching also allowed a high yield from the sheet of material being worked, which made the process extremely cost-effective when compared with other technologies. 

The thin flat springs used in the hearing aid had to be produced with extremely low tolerances, and for this application, Precision Micro achieved the standard tolerance of ±25 microns. To accommodate these fine tolerances, various tooling iterations were required which was possible to do cost-effectively with the photo-etching process, as the tooling is digital. This means that multiple tooling redesigns can be produced not only much more cheaply than processes that require physical metal tooling, but also extremely quickly. 

With so much of the success of mass production of parts using photo-etching — such as the flat springs in this particular hearing aid application — being down to the expertise at the digital tooling stage, it is important that medical device OEMs partner with their chosen photo-etching provider early in the design stage in order to maximize the time-to-market savings that are inherent in the process. 

It is the case that throughout history, medical advances have been made due to technological innovation, and in effect, photo-etching is just another technological innovation that enables the design, manufacture, and clinical use of groundbreaking medical devices. Not only does the technology allow for the manufacture of complex precision devices, but in many instances it is the only metal processing technology that can cost-effectively and repeatably produce mass produced parts to the standards necessary in many medical applications.

Albert Tsang is technical manager, Precision Micro

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