The City of San José faces the challenge to preserve one of the most important estuaries in the United States alongside a socially and economically complex urban community. Over one million residents and 16,000 commercial and industrial businesses, including many of the leading high-technology firms in the country, are located within the San Jose/Santa Clara Water Pollution Control Plant (SJ/SC WPCP) service area. The City operates the SJ/SC WPCP according to the terms of its National Pollutant Discharge Elimination System (NPDES) permit. According to these terms, the City is responsible for limiting the discharge of pollutants to the South San Francisco Bay (South Bay). Copper is one of the metals of concern that point and non-point (storm water) sources strive to reduce.

In the City of San José, Pollution Prevention Strategy for a Clean Bay, Including Proposed Local Limits for Copper, Nickel and Cyanide, October 1994 Report, the City committed to the Regional Water Quality Control Board (RWQCB) to perform a study on direct metallization technologies. The study investigated the potential for these technologies in reducing the amount of copper discharged to the sewer system by printed circuit board manufacturers.This study also compares this new technology with the traditional electroless copper system in different areas, including performance, economic impact and pollution prevention. The City completed and published the Direct Metallization Report in July 1996. In the report most through-hole plating technologies replacing electroless copper were considered.

For this project, vendors and PCB shops in the San Francisco Bay Area were contacted. Some informational sampling was also done. The project involved three tasks:

1) Researching Literature: An extensive search was conducted; however, it provided fewer than ten articles on the subject. This is an indicator of the relative infancy of this technology. This search also investigated and compared the different manufacturers and the technologies used in the direct metallization process.

2) Investigating Companies: This task included compiling the names and contacting the different companies that employ this technology. It also involved the investigation of the companies' product lines and customer base. Some effort was also put into understanding any failure of this technology in some of the companies and the reasons for the failure. This task also included a survey of PCB manufacturers in the San Francisco Bay Area.

This task was completed with cooperation from local companies that were either using direct metallization or were in the process of installing it. Comparison was based on the performance of these two different systems. Copper discharge and wastewater flow were quantified accordingly. Field samples and historical records were collected and documented as needed and where possible.

Due to the increasingly strict environmental standards and safety issues, PCB manufacturers are looking for methods to reduce waste and eliminate hazardous chemicals. These and other business motivations have influenced the development of new fabrication technologies in the PCB industry. The electroless copper process for through-hole plating has been identified as a source for potential waste reduction. As a result, many vendors have developed alternative processes to traditional electroless copper through-hole plating.

Direct metallization processes eliminate the use of formaldehyde and chelated copper containing electroless baths. Due to the reduction in the number of rinse stages, direct metallization processes may also reduce overall water usage. Reduced flows may in turn reduce the volume of metals discharged into the sewer system. The replacement of the electroless copper process may also result in savings to the PCB manufacturer.

A second motivation for direct metallization is the increasing demand for PCBs. Paralleled with the rapidly increasing demand for electronics, there is a need for larger throughput and volume from the shops. PCB manufacturers are looking for faster methods of production while making the process easier, more reliable and less expensive. Some direct metallization vendors claim to have developed such processes and machinery.

There are many different vendors of direct metallization technologies. Although each vendor process is unique and has a slightly different approach in using the fundamental principles of direct metallization, all existing systems fall into one of the following four categories: Carbon Systems, Palladium Systems, Conductive Polymer Systems and Non-formaldehyde Electroless Systems.

Process equipment manufacturers, in close association with the vendors, produce machinery that employs the vendor’s technology. Note: Due to the extreme variability of the PCB industry, a specialized and unique process line is usually required for each PCB manufacturing site. Development of such a unique line can be time-, resource- and cost-intensive.

The purpose of the direct metallization survey was to collect information and compare the opinions of the PCB manufacturers regarding direct metallization technologies. A short, two-page survey was drafted and sent to 68 Bay Area PCB shops. Facilities in the Bay Area were targeted since a larger scope was beyond available resources. This survey was conducted in the Summer of 1995.

A total of 60 surveys were completed and returned. Of these, 59 were applicable to our study. The following charts show the size classification of the 59 returned surveys and their status in relevance to installing direct metallization processes.

At the time the survey was conducted, direct metallization had been implemented by eleven companies in the Bay Area. Currently seven manufacturers are still using it, while the other four have reverted back to electroless copper.

A total of 46 shops commented on the advantages and disadvantages of direct metallization and electroless copper. In analyzing the data collected, each shop listed multiple advantages and disadvantages that were either predicted or have been experienced in the past. The most prominent are listed in Figure 3.

Quality, for the purposes of direct metallization process evaluation, is defined as the ability of the plated surfaces within the drilled holes to meet predetermined specifications and the ability to satisfactorily interconnect with the circuitry on the surface(s). This is measured by, but is not limited to, thickness, uniformity, absence of defects and reliability. It can be influenced by, but again not limited to, raw materials, chemistry, earlier processes and process settings. It can be measured in the laboratory by simulated tests or in situ samples from process.

The companies interviewed detected some problems such as voids, outgassing, interconnect problems and failures at the knee.

Most vendors provide conveyorized direct metallization systems. These systems have the primary advantage of reducing the time it takes to produce through-hole plated boards. Companies have often been able to eliminate an entire shift by going from a manual to an automated line; this advantage is fairly universal among the different direct metallization technologies observed for this report. This can translate to quicker turn-around time and savings in labor costs. Where the batch electroless process was automated or a good job of optimization of the manual process had occurred, the improvement in process time was less dramatic but significant. It was also noted that the success rate for sites installing direct metallization with conveyorized lines is higher than for sites going to a batch, vertical system.

Several local PCB manufacturers discovered that defects with through-hole plating became harder to spot. Some shops have had increased difficulties detecting voids and faulty connections after switching to direct metallization. Some shops have reported that visual inspection used to evaluate electroless copper deposits could no longer be conducted with direct metallization. The information collected reflected the difficulty in board inspection as a major disadvantage of direct metallization.

The direct metallization processes have had better success on double-sided rigid and flex boards than with the multilayer boards. Manufacturers of multilayer boards are still encountering problems. The problems include incomplete removal of intermediate coating during microetch process and outgassing from voids. Some were unable to produce parts that could meet Milspec-level inspections because of carbon residues remaining on the copper inner layer surfaces.

One of the main motivations for the installation of this technology is its feasibility and cost effectiveness. The cost of these systems varies depending on the configuration and the equipment used in setting up the process. Using existing tanks as a vertical, batch-type direct metallization process, presents a much smaller capital cost barrier than the conveyorized versions. However, based on survey results and the information collected, the use of conveyorized systems is greatly preferred by PCB manufacturers. Apparently the board throughput benefits of a conveyorized system, in terms of speed and cycle time, are considerable and overshadow the advertised benefits of formaldehyde elimination and improving the board’s ability to resist thermal stress failure.

The high cost of a conveyorized system is clearly a major barrier for shops interested in direct metallization. Although small- to mid-sized production or prototype shops can invest in the technology for approximately $50,000, the mid- to large-sized manufacturers spend proportionately more for such systems. It is important to realize the need to invest in high-quality automation instead of gambling on a questionable conveyor system.

Another related cost in set-up of the direct metallization process is running systems in parallel. The majority of implementations occurred at Bay Area sites where the systems, electroless copper and direct metallization, were run in parallel. Therefore, the costs associated with finding space, lab support, waste treatment and other costs for running both processes should be planned for several weeks.

As for labor costs, it was noticed that equipment maintenance costs increased. This is reasonable to expect when converting from a manual to a conveyorized system. On the other hand, the cost for production staff dropped due to the advantage of improved cycle-times; where an electroless copper line was operated for two or three shifts, a conveyorized direct metallization line typically operated for half that time. The labor savings were less significant where the electroless copper was originally an automated line.

Environmental issues were an early motivation for development of this technology. Hazardous chemical baths, high water usage and high metal waste discharge are the three main issues targeted for minimization or elimination. Direct metallization eliminates formaldehyde, trace cyanide and other hazardous wastes from the through hole plating process. It may also reduce the amount of water usage in the process and the amount of metals in the wastewater generated.

One of the main environmental benefits, and a driving force in the use of direct metallization, is the elimination of formaldehyde. It is a main component of the electroless copper process. Formaldehyde is classified as an irritant and potential cancer hazard. The limits set under OSHA’s regulations are difficult to maintain with the traditional electroless copper process.

Due to changes in the chemicals used in the process, chelates and copper waste bail-out are minimized or eliminated, thus reducing waste treatment and hazardous material handling. The decreased number of rinses in direct metallization can also reduce overall water usage. In some cases, the elimination of the electroless copper removes a heavy burden from the waste treatment plant by eliminating one of the worst chelated products from the waste stream. When the chelating agents get in the wastewater they tend to prevent metals from precipitating, rendering the pretreatment process more difficult. With no EDTA to contend with, the pretreatment chemistries can be reduced drastically. In one case, these chemistries were reduced by 25 percent. In another, there was no reduction in the wastewater used because the rinsewater had already been optimized and the amount of metals discharged also increased due to the need to treat the new micro-etch used. The micro-etch that was previously used with the electroless copper could be recycled on site. Since most Bay Area companies suffered through drought conditions for several years and were pressured by water retailers to reduce use, most PCB manufacturers have implemented flow reduction measures in their facilities. Anticipated savings and benefits from easier-to-treat and reduced wastes were a primary advantage cited in the discharger survey.

The conclusions made from this study are based on the responses taken from the surveys, available literature and research on this subject, the direct metallization vendors’ literature, and information collected from interviewing people in the PCB industry.

The latest generation of direct metallization technology is still in its infancy, and use in the PCB manufacturing industry is just beginning to spread. In contrast to the electroless copper process that has been traditionally used, this new technology needs to be customized for the PCB manufacturer’s site, process, chemistries and products. The future success of direct metallization relies on product reliability and quality and customer acceptance, both of which require further work.

When installing a direct metallization processes, the whole PCB manufacturing process needs to be evaluated. In some instances, other process steps such as the electroplating chemistries and the microetch affects the product, in contrast to what the vendors claim. The PCB manufacturers have to experiment with the direct metallization process and adjust it to the specific line for their particular products. This has proven more successful than following the vendors’ recommendations since the vendors are just as inexperienced in the implementation of these processes as the PCB manufacturers.

The direct metallization technology might prove to be a very viable option in this industry, but at this time it still needs to be investigated on a per-site and per-product basis. Quality concern is the major obstacle preventing the widespread use of this technology. Although some sites have experienced great success with quality, many are having problems meeting acceptable standards. Once technically proven, this relatively new process will prove to be a better option for the environment.

John Mukhar, P.E, associate sanitary engineer, is a manager in the Environmental Engineering Section at the City of San José Environmental Services Department. He has been with the City for five years. John holds both Bachelors and Masters of Science degrees in environmental/civil engineering. He worked as a facility engineer and in consulting prior to joining the City of San José.

Acknowledgment

The author wishes to acknowledge the people who worked on completing the Direct Metallization Report: Sami Areikat, Bob Chessman, Mharr Dirige, Jack Lin, Pascal Roubineau and Alan Young, all of whom are with the Environmental Enforcement Division of the Environmental Services Department of the City of San José.