Circuit Board Design Tips for Hard or Soft Gold
At Bay Area Circuits, we frequently receive questions regarding how to specify the location, amount and type of gold finish that should be used in a particular circuit board design from PCB designers.
We asked our own Matthew LaBar (Bay Area Circuits Account Manager & great all around technical resource!) to provide a few circuit board design tips that will help you make the right choice on your next design project.
Due to the specialized nature of hard gold and soft gold surface finishes, many designers never encounter the particular challenges associated with these surface finishes. As a result, the first build for a hard or soft gold PCB can often be cumbersome and even surprising.
Although hard gold and soft gold have different applications, they behave similarly for the purposes of manufacturing. With both finishes, the required gold thickness is an important piece of information for the board manufacturer. If the gold is not thick enough, then the board may not work properly. If the gold is too thick, then you may spend unnecessary money. The typical gold thickness for hard gold applications is 30 or 50 millionths of an inch, while gold thicknesses for soft gold range from 20 millionths of an inch to 50 millionths of an inch, depending on the wire bonding process. Because there are so many possible gold thicknesses, the designer needs to call out his/her preferred thickness to make sure the manufacturer builds the right board for the right price.
Gold thickness is not the only cost driver; in fact, copper area is usually a bigger factor because of full-body plating. Full-body plating, or full-body gold, means that all outer layer copper will be plated with gold and results from the electrolytic process required for both hard and soft gold. In electrolytic plating, a current must be running through the plating surface for the gold to plate on. Therefore, hard gold plating and soft gold plating are both done before the etching process—if not, there won’t be a connection to plate any of the pads. But that means that all of the outer layer copper gets plated, leading to full-body gold. The full-body gold, combined with the high cost of gold, means that any extraneous copper can add a lot of cost to the PCB. Ground planes on outer layers can easily triple the price of your PCB, so make sure to minimize outer layer copper when designing a board with hard gold or soft gold.
These circuit board design tips can greatly reduce cost and simplify manufacturing. If designers make sure to specify their required thickness and avoid unnecessary copper on the outer layer, most problems from hard gold plating and soft gold plating can be eliminated.
- Choose the right gold thickness for your application; too little gold may cause functionality issues while too much gold may increase cost unnecessarily.
- When designing for full body gold, limit the copper on the outer layer as much as possible to control costs, as all outer layer copper will be plated with gold.
Matthew LaBar is an Account Manager for Bay Area Circuits, Inc., and owns Scalar Manufacturing, an electronics manufacturer representative firm.