Precision Plating of Electronic Components

Article From: Products Finishing, , from Products Finishing

Posted on: 7/1/1996

Electronics plating may appear simple, but getting it right for each customer is an accomplishment...

As the coil of metal turns, it releases an intricately shaped ribbon of parts. The ribbon progresses through a series of cleaners, rinses and plating baths. As it winds around a spool at the opposite end of the plating line, there is a tiny spot of gold on the tip of each part. It may sound simple, but plating electronic components is anything but easy. Ask the Belmonti family at Precision Plating Company, Inc., in Chicago, Illinois.

"Electronics plating involves high technology, tiny parts, extensive engineering, a clean environment, efficiency, precious metals, a commitment to quality and customer satisfaction," noted Jeff Belmonti, national sales manager for the family business.

Precision Plating has been in the business of precious metal plating since 1904, when it plated picture frames with gold for Marshall Field's department store. Owned then by the Zacharais family, business increased during World War I along with the company's expertise at precious metal plating.

As personal computers and other electronic devices debuted in the general consumer market, the company's expertise with precious metal plating was in demand. However, during the economic recession in 1989 the original owner's family decided to sell. That is when James Belmonti, who was then vice president of technology, decided to buy the company. His vision was to be the provider of choice for the application of highly engineered plated finishes that result in 100 pct customer satisfaction.

The company's dedication to high-quality, high-technology plating has earned it the business of some notable, world-class electronics manufacturers: IBM, Delco, Winchester Electronics, AT&T, Berg, Bourns, Breed Automotive and Motorola.

President James Belmonti is the driving force behind the success of the company. "He loves plating, pure and simple," stated his son Jeff. "He wants to give the customer the best finish for its part at the best price.

"We found that many of the engineers that specify certain finishes on the electronic parts do not understand what we do," explained Jeff. "They are concerned about cost, so we show them how costs can be reduced through selectivity of the deposit."

To help customers understand how continuous selective electroplating works, James Belmonti developed a manual on the various methods. Within the manual is an example of a plating specification sheet that is essentially the customer specification, translated into Precision's computerized color-coded format. This specification drawing can be pulled up on computers in the lab, on the plating line, in the accounting office or at any other station in the facility. A process control plan for each job also is established and can be pulled up on computers throughout the plant.

The manual includes descriptions of the plating processes available to the electronics industry. The company plates hard and soft gold; palladium/nickel and palladium from AT&T Nassau Metals; copper, nickel sulfate and sulfamate and sulfonic tin/lead solutions. The recent growth and interest in palladium/nickel finishes, plated by Precision since 1983, is supported through the use of electroplating chemicals and services of AT&T Bell Laboratories. The following are comprehensive excerpts from Mr. Belmonti's manual describing each technology.

Continuous (reel-to-reel) plating provides a cost advantage because the process selectively plates only a designated area. The metals plated include gold, palladium/nickel, palladium, copper, nickel, tin and tin/lead solders.

The principle of reel-to-reel plating is deceptively simple. In reel-to-reel plating, unplated material is unwound from a feed coil and conveyed through a series of processing stations and recoiled on a take-up reel. Because of the shape, size and fragility of the material being plated, and the number of difficult and complex plating specifications, it is a relatively complex operation that must be customized for each application.

In reel-to-reel plating the strip material is conveyed through the equipment horizontally or vertically. A processing (plating, rinse) station has two sections: the upper process cell and the lower reservoir tank. Solution is pumped from the reservoir tank into the upper cell where it flows over weirs and back to the reservoir. Solution heating and filtration is done in the reservoir.

As the plated material leaves each process cell, air knives and/or soft rubber wipers, remove dragout. DI spray rinses follow each process station.

At each processing station, the strip must be made cathodic or anodic. This is accomplished using several types of electrical contact configurations. The contact type depends on part style. A firm contact force is necessary to prevent interruption of current, but not so firm as to damage the part.

Plating lines require emphasis on "one-pass" operations that allow cleaning, rinsing, selective or overall copper and/or nickel undercoats, selective tin or solder and occasionally an electropolishing operation in one run through the line. This requires plating lines of 80 ft or longer.

Continuous controlled-depth plating. This is the simplest method of selective plating. With this method, parts are immersed partially in the plating solution. The height of the deposit is set with adjustable solution-overflow weirs and by the position of the guide sprockets. Some over-plating can occur due to the difficulty of controlling solution levels. This type of plating sometimes requires custom tooling.

Continuous moving-belt mask plating. Belts made of soft rubber bonded to an insoluble metal backing strip prevent the plating solution from reaching the parts' surface except for exposed narrow bands on the parts. The plating solution is jetted from a plating cell through slots in the masking belts, which are firmly pressed against and moving with the strip. Solid material and pre-formed components can be plated with one or more stripes on one or both sides of the strip.

Continuous belt-and-drum plating. With this type of plating a rubber-covered drum masks the back of the strip being plated, and two rubber belts are used to produce the selectively plated stripe. The width and location of the stripe are controlled by the placement of the belts.

This system can also be used for tip plating by allowing the material to protrude laterally from between the drum and the masking belt.

Continuous spot plating (step and repeat). Small, well defined, round or rectangular plated spots are produced with spot plating. To obtain spots in precise locations, pre-punched guide or pilot holes are used. This allows parts (strip) to move continuously through the pre-plate and post-plate sections.

The plating masks are precision molded silicon rubber that are opened and closed using a clamshell-type mechanism. Typically, a 24-inch section is indexed per each movement of the materials. This type of selective plating provides precise location of well-defined and discreet plated spots.

Continuous (brush) plating. With this type of plating, an absorbent medium, such as felt, introduces plating solution only on the required plating area. This medium may be a roller or any configuration that best complements the contact form.

Brush plating limits plating to the raised contacting surfaces of electrical contacts. This method can be used to plate only one or two sides of rectangular connector pins.

Precision Plating also offers conventional rack and barrel plating. A new automated rack/barrel line was recently installed for plating copper, nickel and bright acid tin. The line features plating tanks and rinse stations from Hardwood Line and

Poly Products, Inc. The rinse stations provide extensive rinsing in a single station. This saves money on water and allows for faster plating.

The plating line is controlled by a Geotronics DS4000 control system. The system provides total control of load scheduling, sequencing, hoist positioning, rectifier control, time-in-tank and other operating parameters. By simply "clicking on" the desired plating tank on the computer screen, operators can find out the temperature, time-in-tank and next processing step, as well as the job number for the part.

In addition to the control system on the line, the company has a lab that routinely tests all plating solutions. Some of the equipment includes Hull cells, surface tensiometer, contractometer UV for additives analysis, pH meters, a Perkin Elmer 5000 atomic absorption spectrophotometer, deposit purity, and a Mettler MT-5 scale for measuring products in micrograms up to six decimal places.

Equipment for inspecting plated finishes includes several Fischerscope x-ray fluorescence systems; porosity chambers, contact resistance testers, Steam age solderability chambers, various adhesion testers and other testing and measuring equipment.

All of this helps the company live up to its name and its vision, "To be the provider of choice for the application of highly engineered plated finishes that result in 100 pct customer satisfaction."

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