Beginners guide to PCB manufacturing (25 minute read)

Forward

I began learning about printed circuit boards (PCB’s) when I was a recent hire at Enthone and while I knew much about functional and decorative plating I knew very little about electronics. As I began to probe into how our product lines served the electronics market I found a plethora of quality information dedicated to specific products but little encompassing everything and explaining to a newcomer how the various processes interacted, how our products fit these processes, and what competitive advantages Enthone products offered. To get this information I went straight to our tech service reps and customers who were troubleshooting issues and optimizing processes. Going to the center of activity was able to create this guide to fill in the missing information. Hopefully with this guide, anyone can understand the basics of printed circuit manufacturing and how our company supports this business.

Special thanks to Patrice Dumas, Ken Mckeown and Rudi Reetz for their invaluable input and time, without which this guide would not be possible.

Intro

A printed circuit board is an apparatus used to connect and structurally support discrete components in a variety of electronics applications. PCB’s are thin, planar rectangles constructed using multiple steps in a manufacturing facility or “fab”. First, sheets known as inner layers are laminated together to form the basic structure of the PCB. The resulting laminate is further processed to make the outer surface conductive so that components may be connected electrically from the outside. Finally, a coating is applied to the board to protect it during transport to another facility, where discrete electronic components will be assembled on the board.

Rhodium Process Guide

Rhodium plating is one of the lesser known forms of electroplating. Many factors affect the properties of the deposit and a reliable process will ensure consistent thickness, reflectivity, and adhesion. The fishbone chart below can serve as a guide to eliminate common plating issues found with rhodium.

Electroform it right the first time

Q: I am experiencing blistering when I electroform copper over aluminum substrate. What could be the root cause? 

A: This question came from a company producing tight tolerance parts for radio applications. Before I answer what the root cause was I think it prudent to do a quick overview of the electroform process, shown below. By nature of the process, rework is very expensive; As soon as the aluminum is dissolved the part can no longer be stripped and replated and a new mandrel must be made. Therefore it is critical to ensure that all chemical processes are working properly. By focusing on improving first pass yield the cost of manufacturing can be significantly reduced.

 In this particular case we discovered that oil contamination was the culprit. Although the manufacturer had focused on improving their alkaline cleaning process, drag-out propagated the issue throughout all the plating tanks. Only when proper rinsing (i.e. cascading overflow rinses) was practiced throughout the whole line was the issue resolved.

Adhesion problems bright copper

Q: I plate nickel over acid copper and am having trouble getting the nickel to adhere to the copper plate. The surface needs to be bright as possible as this is for a decorative application. 

A: Excessive brighter level can cause real adhesion problems with many deposits. Whether you are doing bright copper or bright nickel the components that make up the additives tend to inhibit any post treatment, including more plating. I would recommend using a reverse electroclean for 30 seconds followed by an acid dip to remove the brighteners and activate the surface. This will allow you to plate over the copper or nickel without sacrificing aesthetics. You won’t see this problem with chromium systems as the chromic acid will do this job for you.

Black nickel and relieve reject issues

Your parts are doing something...even when you’re not plating 

If you’re doing a plate-and-relieve antiquing process, pay close attention to the following infographic. A customer recently told us of a high scrap rate associated with the following process:

1. Steel substrate 
2. Nickel strike
3. Brass plate
4. Black nickel
5. Relieve for antique look 

We conducted a 3 part experiment focused on the black nickel step and did the following tests:

Trial 1: 3 minutes black nickel plate, rectifier on
Trial 2: 12 minutes black nickel plate, rectifier on
Trial 3: 3 minutes black nickel plate rectifier on, followed by 9 minutes immersion in black nickel black with no rectifier

As you can see, leaving the parts in the bath without a rectifier had an interesting effect and often times stripped off some of the plate that had been electrodeposited previously.