Most people can appreciate the unique value of lustrous yellow gold as a decorative metal for making ornate jewelry and attractive furnishings. In addition to its wide variety of decorative uses, nearly 10 percent of the annual world gold production is for industrial uses, including the manufacture of electronic devices. In particular, gold is the metal of choice for making reliable electrical contacts in connectors and switches due to low-contact resistance and long-term corrosion resistance. However, because of its high demand in decorative applications and its link to the volatile financial markets, gold is an expensive and risky material choice for use in electrical devices. The market price of gold has remained above US$1,000 per troy ounce since 2008, and manufacturers continually look for ways to reduce the amount of gold present in their devices, without sacrificing quality, to decrease financial risk and costs.
In the electrical connector industry, among the precious metals, gold is used most frequently because of its conductivity. Gold is applied electrolytically as the final metallic layer by use of a reel-to-reel electroplating system. In a reel-to-reel setup, gold is applied to all areas of the device that are electrically contacted to the plating solution. Over the years, selective-plating techniques have been developed to limit gold plating to areas only where gold is needed, such as by selective spot plating or belt plating. These techniques physically mask some areas of the connector device from the plating solution, and are meant to avoid wasteful application of gold to areas where it is not needed. These techniques increase the complexity and cost of the production process, and still suffer from precious metal “bleed.” This is a situation where excessive gold is electroplated in areas that are ineffectively masked, and they can account for up to 20 percent of the total amount of gold deposited onto the device. Hence, there is a strong manufacturing need to have a more effective masking procedure that can be carried out rapidly and that offers improved resolution in reel-to-reel production.
Most selective-plating technologies involve a physical barrier temporarily covering the connector device as it moves through the plating solution. Over time, the selective masks physically wear, reducing mask function further. By contrast, inkjet-printed resists offer a freshly applied, strongly adhering layer of material that provides chemical resistance and an effective barrier, completely preventing gold “bleed.” Compared to selective plating techniques, inkjet-masking resists are capable of providing gold savings of up to 20 percent due to bleed prevention alone. Also, inkjet-printed resists eliminate the long and tedious step of physical mask generation as well as downstream gold removal and recovery issues (back-stripping). Overall, these multiple benefits make inkjet printing a more cost-effective and time-saving process than selective masking techniques.
During the past year, Dow Electronic Materials has developed an inkjet-masking-resist technology, LITHOJET™ 250 inkjettable resist, which can be incorporated in reel-to-reel plating lines to mask selected areas of stamped connector reels for gold plating. When configured appropriately, the inkjet tool is capable of simultaneously masking both sides of connector reels with the resist at line speeds of up to 35 feet per minute, saving valuable fab floor space. The coverage zone capability on connector parts ranges from 0.01” X 0.01” to 3” X 3”, with an alignment accuracy of ± 0.004”. The selectivity and accuracy of inkjet technology is a significant advantage over the current selective plating techniques, which are limited to masking only specific types of geometries on the reel.
Schematic showing the difference between the conventional masking (left) and inkjet masking (right)
Most inkjet-resist products are phase-change wax inks or UV-curable liquid inks, but they have drawbacks: They are too soft or they spread too much, respectively. Dow’s LITHOJET 250 inkjettable resist uses a different approach in ink design, combining the desirable attributes of both ink types. Although not truly a phase-change reaction, the cooling of the ink immediately after printing sets it in place and allows the ink to be pinned with little spreading regardless of surface conditions. The ink is hard, tack-free and chemically resistant after UV curing. Hardness measurements are typically 3H to 4H and, as a result, can withstand the wear and tear in the connector production. In addition, the ink is designed to UV cure and strip off in less than 10 seconds to match the reel-to-reel production speeds of up to 35 feet per minute.
Ease of use and processing make LITHOJET 250 inkjettable resist a viable alternative in the reel-to-reel connector-plating industry. It offers a significant opportunity to decrease financial risk and cost, by reducing waste and eliminating the need for recovery steps in the manufacturing flow.