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The Spouted Bed Electrode Plater: Improved Technology for Electroplating Micro-sized Components


George A. Federman and George Hradil

The spouted bed electrode, SBE, electroplating machine was specifically designed for parts with dimensions smaller than 1 cm in any single dimension. The key technology of the SBE plater is the use of a solution jet that circulates the parts throughout the plating chamber during cleaning, activation, plating, and rinsing operations. It is particularly suitable for plating parts that are difficult to plate in traditional equipment, including surface mount passive components, flat parts, leaded components, and pins.

The rapid pace of miniaturization in the electronics and semi-conductor industries has led to the emergence of discrete micro-sized active components such as miniature TO headers, connector clips and pins, and passive components such as chip capacitors, resistors, varistors, and inductors (Figure 1). These components often require electroplating as a finishing step to impart specific corrosion, wear resistance, conductivity, and solderability characteristics. The size of these components has been reduced so significantly in recent years that conventional electroplating equipment technologies are not fully suitable for this purpose. It has even been suggested that the electroplating of these parts is one of the major barriers to further miniaturization. It also must be noted that electroplating of these parts is the final manufacturing step before the parts are shipped to the assemblers. Failure of the parts at this stage due to problems that occurred during electroplating is very costly.

The SBE plating chamber offers electroplaters an effective tool for plating this new generation of parts, owing to its fundamentally different technology from barrel plating. It does not suffer from problems such as:

  • Poor solution transfer between the barrel interior and the exterior solution that can lead to defects in deposit morphology caused by depleted or contaminated solutions;
  • minimal load mixing within the barrel during the plating process, resulting in broad part-to-part thickness distributions;
  • fouling of small parts in the barrel wall and seams, causing unplated or overplated parts;
  • coupling or twinning of parts due to the low mixing rate of parts within the barrel; and
  • formation of metallic nodules in the barrel screens, resulting in high barrel maintenance costs.

A more detailed description of the SBE plating chamber is necessary to understand how the equipment provides the aforementioned benefits. In the SBE plater, the parts are retained in a vertical cylindrical vessel with a conical bottom section (the plating chamber). The electrolyte (or rinse/cleaner/activator) is introduced into the vessel as a high-velocity jet at the bottom of the conical section of the plating vessel. The bed of parts on this cone is moving downward and radially inward towards the solution jet.

As the parts enter the electrolyte jet stream, they are entrained in the jet and are forced upwards within an interior shaft in the plating vessel. The parts then contact a deflector plate and disengage from the jet in a region just above the interior shaft. They then move radially outward and downward toward the bottom conical section to once again join the packed bed of parts flowing across the current feeder (see Figures 2, 3, and 4). The parts are plated only in the conical section of the vessel, where they form the moving packed bed that comes in contact with the current feeder.

Load Volumes

The standard SBE chamber can accommodate loads of 50 to 500 ml. For loads of less than 50 ml the load volume should be increased by adding media. A maximum load of 500 ml may seem small but the SBE is designed to plate small parts where relatively small volumes translate into very large numbers of parts. For example, 135 ml of 0201 case-size capacitors is over two million parts.

Solution Flow Rate

The solution jet velocity entering the plating chamber can be adjusted from 15 to 60 liters per minute through electronic control of the rpm rate of the solution pump impeller. The SBE plating chamber has an internal volume of 3.7 liters, so the solution exchange rate can be as high as 12 turnovers/minute. The electrolyte flow rate is adjusted according to part size and density; larger, denser parts require higher liquid jet velocities to achieve entrainment and particle transport.

Anode Design

A circular anode basket, or insoluble anode mesh, surrounds the plating head and current is conducted from the anode to the cathodic load via the mesh-enclosed openings in the chamber wall. Solutions entering the vessel via the bottom electrolyte jet exits through these mesh-enclosed openings on the side of the chamber.

In-process Sampling

The SBE plating chamber is not fully immersed in the bulk electrolyte within the plating tank. The top of the chamber is out of solution, and contains openings that allow the line operator to take small samples of the load during the plating process to check for deposit thickness. Sampling takes place without interrupting the plating process.

Part Discharge

Parts are discharged from the SBE plating chamber by removing the internal deflection assembly and disconnecting the injet tube from the plating chamber. Parts then flow downward along the chamber’s bottom cone into the customer’s capture vessel. All SBE platers are equipped with a DI water spray gun to help flush the parts from the plating head.

Transport of Plating Chambers

The plating chamber itself is transported much like a barrel is moved throughout a line, from tank to tank. Transport of the plating chamber(s) can be manual, semi, or fully automatic. Line configurations can be fully customizable to allow plating of several different metals on the same line. Metals that have been successfully plated in the SBE plater are copper, nickel, tin, tin/lead, gold, silver, and palladium.

Advantages

Deposit Quality

High-quality electroplating requires that electroplating solutions surrounding the parts be as “fresh” as possible. Plating from depleted solutions can result in dendritic or porous deposits that will fail deposit performance tests for solderability and corrosion resistance. The high-velocity solution jet design of the SBE plater insures that plating takes place under optimal plating electrolyte conditions.

Conventional barrel plating has no such guarantee, as the high mesh count of the barrel sides restricts solution interchange. Exterior solution spargers directed at the barrel are also relatively ineffective, as the load in the barrel acts as a barrier to allowing the fresh solution into the barrel.

Rinsing in the SBE plater is significantly improved as well, as rinse water is circulated through the plating vessel at the same rate as the plating solution. Better rinsing reduces chemical contamination caused by drag-in of upstream, incompatible chemical processes into the plating solutions, and provides a chemical-free surface on the finished part as it exits the final rinse stage.

Plated Metal Distribution

Unlike conventional barrel plating technology, where the parts move only radially and not laterally within the barrel, the design of the SBE plating chamber ensures that all of the parts experience identical trajectories within the SBE plating head. The circular anode basket surrounding the plating chamber maintains the same distance between the anodes and the cathodic moving packed bed of parts, resulting in a uniform plating current density. Therefore, plated metal distributions are significantly improved compared to conventional barrel plating. This is especially important when plating precious metal, as the metal savings can be substantial. It also allows the plater to target lower mean plating thicknesses without fear of producing parts that do not meet minimum customer thickness requirements. Reducing the plating target thickness will result in reduced plating times and improved machine productivity.

Fouling of Parts

The SBE Plating chamber has no moving parts (gears, doors, or danglers), and no seams/gaps to entrap micro-sized parts. The SBE plater eliminates unplated parts, or, just as detrimental, contamination of parts with previously processed parts that have been entrapped in prior barrel loads.

Coupling of Parts

Part singularity is extremely important when plating small components. The high rate of solution/part agitation throughout the SBE plating chamber helps to insure that the parts do not plate together in lumps. The movement of the parts against the primary deflector in the plating chamber also helps to keep the parts separate. Parts are not damaged by contact with the deflector, as the deflection takes place under solution, and the force of the impact is very low because the parts have little mass.

Maintenance

It is common practice when barrel plating small parts to perform periodic removal of metallic nodules that have plated onto and into the barrel wall screens. The barrels can be damaged during this removal process, and the labor to repair the barrel screens must be taken into account. This will not happen in the SBE plating chamber. Parts coming into contact with the solution output screens are not part of the packed cathodic bed, so there is no possibility of plating nodules onto and into the screens. There is little to no normal maintenance on the plating chamber. Plating chambers that have seen continuous use for the past three years are still in production, with no maintenance other than occasional stripping of the current feeder.

Miscellaneous—Media Usage

When plating composite parts with conductive and non-conductive portions such as SMT passive components, the SBE requires substantially less media than is typically used in barrel plating. In general, it has been found advantageous to use media in volume ratios as low as one to four media to parts; the opposite ratio is often used when barrel plating. Technic has developed proprietary shaped and sized media (patent pending) specifically for the SBE, which allows the used of such low ratios of media to parts. Typical spherical media (shot) used in barrel plating will not work for plating SMT components in the SBE.

Reduced media usage will lower costs, especially when plating precious metals. It also improves the productivity of the plating chamber, as more parts, rather than media, are used in a given load.

Sampling

Having the ability to sample the load for deposit thickness without interrupting the plating can reduce cycle times and plated metal costs, especially when plating new part designs for the first time. Job shops receiving many different types of parts on a regular basis have found this attribute extremely helpful.

Results

The SBE plater was first introduced to the small passive SMT component industry in 2001. It has since found use in other applications, and most customers that purchased their initial SBE Plater have subsequently ordered larger production machines to replace some or all of their barrel lines. Some typical results from production are seen in Table 1.

Table 1: Typical Results
Large Chip Resistors (2020 case size: 0.20 × 0.20 inches)
MetalSBEBarrel
 Min. (µi)Max. (µi)Avg. 
(µi)
Std. Dev.% CouplingMin. (µi)Max. (µi)Avg. 
(µi)
Std. Dev.% Coupling
Ni10315812216.8 10140918357.8 
Sn3523783678.2224245134338.911
Miscellaneous Chip Capacitors
Case Size020104021812
EquipmentSBEBarrelSBEBarrelSBEBarrel
Chips (ml)303200200170200
Media (ml)659750–100400170400
Ni (amp-hr)406035801015
Mean (µi)9970101959293
Std. Dev.11.213.94.313.13.28.5
Sn (amp-hr)254525401312
Mean (µi)240201228234270264
Std. Dev.24.93412.126.99.820.1
SBE-Plated Ni/Au-Plated Socket Connector Pins
MetalPlating Time (min)Min. Thickness (µi)Max. Thickness
(µi)
Mean Thickness (µi)Std. Dev.
Ni301651911738.3
Au3089104974.6

 

George Federman graduated from Dartmouth College in 1976. He worked in the plating industry since 1983, and holds two patents in high-speed tin plating technology. He joined Technic Inc. in April 2001 as vice president, process development, Advanced Technology Division. He was the recipient of the AESF’s Frank E. Lane Industrial Achievement Award in 2002. Federman can be contacted via e-mail.

George Hradil graduated from Brown University with a PhD in chemical engineering in 1991 and is an adjunct professor of chemistry at Brown. He holds four patents, with several additional patents pending. Hradil joined Technic in late 2000 as senior research engineer. He developed SBE technology and allied tin chemistry. He can be contacted via e-mail.

 

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