Progressive stamped parts sometimes require a top layer of material over the base metal to accomplish a specific function, such as solderability, corrosion resistance, enhanced thermal or electrical conductivity, or appearance. Electroplating is a common way to apply material and is often efficient and cost-effective. In this blog, we’ll look at how electroplating works, and in part two, we’ll focus more on two of the most common methods, plus an alternative to plating that’s worth considering too.
Plating Basics
Plating is the process of coating parts (or in some cases base material blanks) by immersing them in an electrolytic solution. Two electrodes are placed in the solution: a cathode (i.e. negative charge) and an anode (i.e. positive charge). The anode is a solid bar made of the plating material (e.g. tin, nickel). Electrical current is passed through, creating a chemical reaction that causes positive ions of the plating material to adhere to the parts. Electroplating processes are a closed loop, in which water is filtered and reused to the greatest extent possible.
Common plating coatings include:
- Copper
- Tin
- Gold
- Silver
In addition, tin and nickel can be applied with either a matte or bright finish, depending on the desired effect. Sometimes there are multiple reasons for plating. For example, only the tips may need to be soldered but you may still want corrosion protection on the body.
To prepare stamped parts for plating, they are washed in an acid bath to remove any oils, grease, or oxidation from the stamping process. An additional bath in an undercoating medium adheres to the base material, which improves the bond with the plated coating.
Thickness of the coating depends on how long the parts are held in the bath (i.e. dwell time) as well as the complexity of the part geometry and features. These can also affect how even or uniform the coating is. Additional factors like bath temperature, electrical current, and the metals used also impact plating. Customers can choose between all-over or selective plating, and barrel vs reel to reel application methods.
Inspection
The inspection process for plated material is largely the same for both barrel and reel to reel methods. Random samplings of parts from each batch are usually checked. Methods and testing may include:
- Visual inspection. With the naked eye and under magnification looks for the required coverage and quality of the plating, consistency without any gaps or exposed base material, and adhesion without any peeling or cracking.
- Measurement for uniformity. Parts are measured, often with x-rays, to examine the thickness of the plating. Note that this is in addition to any post-plating measurement of dimensions for critical features.
- Measurement of thickness. This is important for insertion terminals and parts that must fit inside another part, especially in areas prone to dog boning. In addition to measurement, they may be tested with an attribute gauge like a go/no-go block.
- Solderability or reflow testing. This is critical to ensure proper adhesion in assembly. For example, a part might be dipped in solder only to a certain depth based on what area of the parts is to be soldered, as noted on the print. The first 0.100” of a leg on the part must be tested because that will be the insertion depth in the final assembly.
A stamper that has experience plating small and miniature parts can discuss your options for plating – be sure to read the second part in this series on plating and contact us with your plating questions. We’re always here to help.