Surface roughness can originate from a number of sources; imbalances in the organic additives and improper filming of the copper anodes are key contributors.

In this month’s column, the subject of surface roughness and some lesser-known plating anomalies are discussed/examined. In general, surface roughness is often attributed to particulate matter that is not being filtered from the plating solution; however, roughness can also be caused by a number of other factors. A few of these factors are shown below, with a brief discussion of the root cause or causes of the roughness.

In FIGURE 1, the plated circuit trace is excessively roughened. Upon further examination, it is quite clear that the cause of the rough deposit is residues that remained on the surface of the base copper. Perhaps the team should look carefully at all rinsing and filtration steps leading to the electrolytic copper process.

A common anomaly is seen in the form of a raised area in the electrodeposited copper. This, of course, should be considered a rough deposit. At first glance, the operators may assign the cause to a low concentration of the organic addition agent. Typically, when that assumption is made, the reaction is to add more organic addition agent to the plating solution, but that will cause additional harm to the functioning of the plating solution.

On occasion, one gets a call from a frantic PCB fabricator describing a situation one could call “stringy nodules” or “hairs” as seen in FIGURE 2. Obviously, without first seeing the actual defect, the image that this conjures up can bring about a long brainstorming session as to the root cause of the anomaly.

These stringy nodules have their origin, usually in one of three areas:

• organic contamination in the copper plating solution
• improper brightener and carrier concentrations
• improperly filmed anodes.

It is unlikely that particulate matter floating around in the plating solution causes these stringy nodules, unless the copper anodes are not filmed up properly. In other words, the success of acid copper plating depends in part on the uniform corrosion of the anodes during electrodeposition. In order to insure this, the uniform black film must be present on the anodes, and this film should not be disturbed once it is formed. If the film is not forming properly, one may expect to see these types of nodules, as well as issues related to excessive consumption of the organic addition agents (brighteners, etc.). This will cause the various components of the additives to be out of balance, which will lead to plating anomalies such as stringy nodules and roughness.

A summary of the causes of the various plating anomalies presented in this article is:

Debris

• poor anode quality
• poor filtration
• ASF too low or high
• particulate material on substrate prior to entering bath and/or in bath

• poor upstream processing
• weak pre-cleaning
• strings
• organic contamination
• improper brightener and carrier concentrations
• improperly filmed anodes.

Remember, surface roughness can originate from a number of sources, including organic additive imbalances and improper filming of the copper anodes. Certainly, good troubleshooting starts with a thorough investigation of the plated surfaces, the pre-plate conditions and the potential for particulate matter that, for some reason, is not removed by filtration. 

Michael Carano is global manager for strategic business development at OM Group, Inc. and can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..