In past articles, we’ve discussed many aspects of plating quality, the intense commitment it takes to control it, and the variables that affect it. Today, we’ll be talking about a key factor that influences plating quality, and the long-term performance of gold and nickel-plated electronic components: porosity.
Porosity refers to microscopic defects in the plating of the part. These defects can not be seen by the naked eye. Over time, porous components are much more likely to corrode and cause other issues, leading to eventual failure and even costly damage to other components.
Causes and Types of Porosity
To prevent porosity and the potential headaches it produces, we must understand what causes it. Turns out that numerous factors in the manufacturing process can do so. These include problems with the part surface (such as tool marks, pits, etc.), improper surface preparation, and plating solutions that are not properly maintained. Another culprit is insufficient plating thicknesses.
There are two types of porosity found in gold and nickel-plated parts: active and passive. Active pore sites show corrosion through the plating and into the base material. This type of pore allows corrosion products to spread on the contact surface. Passive pores are observed in the gold plating (top layer), but do not penetrate the nickel plating or barrier layer.
Acceptable Porosity?
Not all pore sites pose potential mechanism failures. For example, in a harsh environment, especially where chlorine and sulfur are present, there is a potential for corrosion creep. If there is a pore site on a mating contact, but most of the interface is properly gold plated and the environment is benign, there may be no adverse effects. The primary factors in determining if porosity will cause failures are whether the pore is active or passive, its location, shielding features, and operating environment.
Avoiding Porosity
To guard against porosity and the potential for corrosion, resulting in increased electrical resistance and field failures, it is important to remember that pore sites increase as plating thickness decreases. It is essential to start with clean, defect-free parts. The underplate should be a minimum of 50 microinches of a stress-free, ductile nickel to ensure against cracking. The gold thickness should be at least 30 microinches, but a thinner deposit can work if mating cycles are less than 10.