When manufacturing critical components, quality is of utmost concern. We have talked in the past about stringent quality certifications – what it takes to earn and maintain them. Today, we will review specific quality factors and how they are measured or tested.
Process controls and bath maintenance are key factors in ensuring plated parts meet required specifications. Quality is baked into every step of the process. However, variability occurs as unexpected things could happen along the way. This is why it’s important to make sure parts meet the requirements before being shipped. After plating is completed, several tests and procedures are employed to verify the integrity of the plate.
This begins with a Visual Inspection of the parts. A quality technician examines the surface of the parts closely, usually at 10X magnification. They are looking for uniform plating, completely free of nodules or voids.
Adhesion – is checked by bending/fracturing/crushing parts. During these tests, the finish must not crack off or peel – it should stick to the parts regardless of the destruction brought upon them. Often, a tape test may be used. Here, tape is applied then pulled to make sure plating doesn’t peel off. Simple, but effective.
Thickness Testing – As parts continue to decrease in size, mating tolerances, especially for connector parts has made controlling thickness imperative. Thickness testing is done by XRF equipment. It’s a non-destructive technique that uses x-rays to determine the thickness of the finish. Most units are capable of measuring thickness of multiple plating layers. Some units can also test for PPM’s of lead in a tin deposit, which is important when RoHS compliance is required.
When dealing with precious metal plating, controlling plating thickness has a significant impact on cost.
Porosity Testing – is done to determine if the plate has pores. These must be avoided since pores allow base material to migrate to the part’s surface and cause corrosion failures. Depending on the metals plated, there are numerous porosity tests available. The most common are nitric acid, nitric acid fumes, gel porosity and mixed flowing gas testing.
Salt Spray Testing – is another way to make sure plated parts meet the required corrosion resistance. The parts are put into a test chamber, then subjected to misty salt water. Essentially, it’s an accelerated test to help verify the integrity of the plating. Note that it does little to predict how the surface will resist corrosion, since it’s difficult to replicate real world conditions in the lab quickly. The test duration may change, but a typical test uses 5% NaCl at 90°F for 96 hours.
Solderability Testing – Many electronic components will get soldered after plating. Testing is required to ensure they will perform as specified. Parts are generally steam aged for 8 hours before testing. They are then control-dipped into a solder pot, and checked for voids or de-wetting.
Special Considerations for Selective Reel Plating
The tests stated above apply to both loose and reel plated parts. With selectively plated reel parts, additional testing is necessary. Plating location becomes a critical factor in the process. The main concern is making sure the required plating is precisely where it needs to be on the finished part. Location control is a must when dealing with precious metals in particular. Not only does the precious metal have to be in the contact area of an electronic component, it must be controlled to keep costs in line.
Another concern for reel plated parts is deformation. These parts are often over-molded or assembled automatically. Since downstream processes operate with very tight tolerances, it is important that parts are not skewed or bent in any way. Location and deformation are often detected with an on-line vision system.