Poor plating adhesion is one of the most common issues that can occur during the plating process. If not noticed and corrected right away, improper adhesion will cause the plate to fail, sooner or later. Thankfully, there are ways to spot these problems early, and process considerations that could be made to avoid them entirely.
What do Plating Adhesion Problems Look Like?
Adhesion failure produces a multitude of unwanted issues such as flaking, peeling, blistering, and delaminating. To complicate the issue, plating issues might not be evident until the component is put into service. Forces such as friction, or expansion and contraction due to heating and cooling, will accelerate the revelation of the underlying defects. While it appears that these factors are the culprits, they are simply accelerating the revelation of an underlying issue.
What Causes Plating Adhesion Failure?
Adhesion failure can be caused by several factors, but can be avoided by incorporating certain procedures during processing. These primarily relate to part cleanliness, improper solution exchange, and other considerations. Let’s take a close look at each.
The first factor involves incoming part cleanliness variations as received from the part supplier. These variations include excessive residual oils left on the parts after machining, excessive residual heat treat scale left on the parts during manufacturing, and oxidation deposits on the surface of the parts. In order to properly coat a part, it must be clean and oxidation free.
Another factor involves inadequate cleaning, rinsing, or activation during the plating process. This can occur due to lack of adequate solution exchange caused by issues such as part geometry (i.e. blind holes, fragile parts, nesting) and poor chemistry maintenance.
How Can Plating Adhesion Failures be Avoided?
Fortunately, these issues can be successfully controlled by using proper risk mitigation techniques. These methods can be performed in many ways based on the part involved and are an essential tool to preventing most plating adhesion related issues.
One simple yet useful mitigation technique involves the use of proper equipment and handling. Examples of this include basket cleaning prior to barrel plating. Basket cleaning prior to plating will remove residual contaminants from depositing on the parts and is a great technique to use when dealing with fragile parts. There are limitations to this, especially when dealing with fragile parts. Aggressive basket cleaning (i.e. excessive agitation) could ding or dent soft brass or could damage the parts by bending fragile parts.
Careful consideration and precaution should be taken before basket cleaning a part prior to plating. For example, plastic baskets are ideal for use on fragile parts in that they reduce damage to parts that may be caused by using a steel mesh basket.
The use of ultrasonics can greatly improve solution exchange by liberating air bubbles in ID and other hard to reach areas of the parts that could otherwise prohibit adequate plating coverage within those areas. There are limitations to this, especially when dealing with fragile parts. Ultrasonics are only effective when processing blind hole parts and are not very helpful when processing solid parts.
Certain plating methods are better suited for handling the job depending on solution exchange requirements. Two methods that excel at this requirement are vibratory and spouted bed electrode plating.
Vibratory plating is ideal for parts with challenging geometries that could lead to adhesion problems. Vibratory excels when processing long fragile parts, since the vibration liberates air bubbles in the ID of parts. This improves solution exchange in “hard to reach” areas, making for a reliable plate.
Spouted bed electrode (SBE) plating offers the most solution exchange to the inner diameters of parts, especially blind holes which is essential to cleaning, activating, and rinsing. SBE’s restrictions are that it is limited to small parts, generally less than an inch in length, and small volumes, less than 500mls.
Rinsing is often overlooked as part of the plating chemistry process, yet vital when producing adequate product and reducing adhesion failure. Rinse waters should have enough flow to ensure they have a continuous flow of fresh water to remain clean. Counterflow rinses are preferred when designing rinse tanks for electroplating use. This reduces residual contaminant deposit when processing parts thus reducing the chance of adhesion failure.
Lastly, having good chemistry is also a great risk mitigation technique. A solid and effective chemistry program is essential to a successful electroplating company. It can be the difference between a successful plated lot and a discrepant plating lot.
Cleaners and activators should have a documented maintenance schedule (i.e. record of chemical additions and changes), frequent temperature monitoring, continuous filtration on all tanks, and a frequent set filter change schedule. These techniques will ensure that the baths are functioning properly and will help maximize successful work output.
The Importance of Quality Control
Platers with strict quality programs in place will usually discover plating issues during production, giving them the ability to make corrections early on. Several testing methods can be used including a bend test, where a component such as a connector pin is bent at 180° and examined closely under magnification. Larger pieces can be either cut or scraped to reveal adhesion problems. Crushing, where the part is simply crushed, or bake-testing, where the part is baked then cooled, are other methods that may be used.
Plating adhesion issues can and should be avoided. Doing so requires that manufacturers source from qualified machine shops, that supply clean parts. It’s also imperative to work with an experienced plater that has a time-tested process and quality program in place to spot these problems early, or avoid them entirely. Doing so will help result in plated components that are durable, reliable, and above all, perform as expected.