Microwave Journal

Understanding Key Electroforming Factors and Why It Might Be Your Only Option

September 24, 2018

Does your product or application call for a very tiny part?  If so, nano-scale electroforming may be your best or even your only option. To find out for sure you will need to talk to someone with expertise and experience in this highly specialized field of manufacturing. To get that discussion started, here is some background on the key factors that help determine nano-scale electroforming success.

Let us start with your design objectives. Typically those include features of precise geometry and tolerances, ultra smooth surfaces and enough durability to withstand the application’s environmental challenges. Whether those objectives can be met within cost and yield targets, depends on a number of process variables—all of which are in a state of continuous flux during production runs and all of which must be tightly controlled based on specific manufacturing best practices. So what are these variables and what’s involved in controlling them? Here are the basics:

Control of Process Parameters During Production Is Critical

At its core, electroforming is an electroplating process. So controlling conditions inside the electrolytic cell while electroplating is taking place is vital. A positively charged metal source is submerged within the cell in a bath composed of various chemicals, including salts. The electrical charge acts on the salts and the metal to ionize the metal so that these ions traverse the tank to a negatively charged metal substrate where the ions reform as metal particles that bond to metal, forming the part. The stronger the current, the faster the ionization, and the faster the part is formed. The part’s shape is determined by a pattern of openings imaged onto the photoresist that expose the substrate’s metal underneath—making it accessible to the suspended metal ions. As more metal is added, the part rises from the metal imaged on the substrate.

Parameters impacting the result of this process include the chemical composition—or balance—of the bath, the temperature of the bath, pH of the bath, room temperature and the bath’s electrical current density. A chemical imbalance can cause stress in the part. Stress is internal pressure within the metal deposit that can cause it to warp, shrink, crack or even break once the part is deployed in your application. Other sources of stress include pH that is too high, current dentistry that is too high and a bath temperature that is too low, as well as too great a difference between bath temperature and room temperature. All these conditions must be strictly and continuously monitored.

Besides adding stress, a chemical imbalance can also cause salt particles to potentially precipitate out of the solution and land on the part, damaging it. Environmental dust presents a similar hazard. Even a 2-micron size piece of lint can do serious damage to a circuit with features in the 5-micron range. That is why the air in plating rooms should be filtered and so should the liquid in the bath. Bath filters should be checked routinely to see that they’re not clogged and that the bath remains clean.

Visual Inspection After Production Is Also Key

Besides monitoring conditions in the bath during processing, it is also important to visually inspect parts after processing. Conditions in the bath constantly drift during production, so quality may drift as well. Visual inspection is the only way to ensure that parts remain within spec. It is possible, for example, after some number of batches that filters will need to be replaced, chemicals rebalanced or the electrolytic cell flushed, cleaned and the bath entirely refreshed. Visual inspection is particularly necessary during early production runs to ensure that process recipes are correct and that finished parts are within tolerance. If they are not then the bath may need to be reformulated, the electrical parameters changed or the recipe revised in some other way.

Of course, all this assumes that a number of other success factors are also in place, pretty much as “table stakes.” Those include state-of-the-art facilities, skilled and experienced process designers, and a commitment to the highest possible quality standards. Manufacturing precise electroformed structure at nano-scale is a rigorous process with little room for error. Success is only possible consistently if all the relevant factors are thoroughly understood and controlled.