PCB Finishes: ENIG, ENEPIG, EPIG, Electroless Gold,
Immersion Silver, Electrolytic Palladium

Related Pages:

• Acid Copper DC Electroplate
• MEC Surface Treatments

New Chemistry Deposits 4-8 µin
Uyemura has introduced a reduction-assisted immersion bath for board customers who demand an immersion gold deposit above the standard 1-2 µin on ENEPIG. Called TWX-40, this is a mixed reaction bath – an elite hybrid – that delivers both immersion and autocatalytic (electroless) modes of deposition.

TWX-40 is a proven alternative to other attempts to achieve heavier gold deposits on ENEPIG, i.e. extending the dwell time in the immersion bath. That practice forces the immersion bath to do what it was never designed to do, and has been fraught with problems, the most serious of which is virtually inevitable damaging of the nickel underlayer.

TWX-40 is a single immersion gold bath with autocatalytic capabilities. Added to a line, manufacturers plating ENEPIG can now deposit 4-8 µin gold in a single step. The standard alternative way to accomplish this is to deposit autocatalytic gold over immersion gold – an additional step, requiring costly additional make-up. For ENEPIG users serving a diverse group of customers, TWX-40 is a proven solution with excellent science behind it. Read more in an article titled TWX-40 Reduction-assisted Gold Bath Meets Demand for Thicker Gold on ENEPIG.

KAT Electroless Nickel/ Immersion Gold (ENIG)
KAT ENIG is the industry standard for producing uniform mid-phos EN deposits with a thin topcoat of immersion gold, over copper substrates. This PCB finish is highly resistant to corrosion, and is both solderable and aluminum wire bondable. It is an ideal contacting surface.

KAT users never have to contend with "dummy plating." They also benefit from:

  • A low-concentration, room temperature, chloride-free catalyst
  • A bath that runs at least 10°F below the competition
  • Compatibility with the newest soldermask technology

Use with the STARLINE DASH Controller. This advanced electroless nickel controller is self-cleaning and self-calibrating. The controller modifies the calibration curve to compensate for the accumulation of bath by-products. It maintains a complete analytical record for SPC charting. MORE

KAT has long been the world's highest-performing mid-phos electroless nickel. That, however, hasn't stopped Uyemura chemists from making it better...

MNK-4 palladium catalyst is an activator for the electroless nickel plating of fine pattern PCBs. While traditional activators often have bridging issues when fine patterns are plated, MNK-4 eliminates the potential for bridging between pads. Stable, chloride-free bath operates between 77-95°F; immersion time is 1-3 minutes. Needs charging less often!

Nimuden NPR-4 is an acid electroless nickel plating bath that has been specially formulated for electronic and PCB applications involving fine line circuitry. The special bath formulation allows the deposition of electroless nickel without bridging. This process operates at lower temperatures, which allows for improved resist tolerance. The bath is very stable, easy to use and is optimized for automatic solution control using the Uyemura STARLINE-Ni controller.

Nimuden NPR-8 is a mildly acidic electroless nickel-phosphorus process engineered for electroless nickel / gold plating to selective PWBs with dry film masking. The catalyst, electroless nickel, and immersion gold components have all been improved for greater productivity, and bath life. The NPR-8 bath is highly stable in continuous use, and the phosphorous content in the deposited film remains constant regardless of metal turn-overs.

NPR-8 is chemical corrosion-resistant, especially against OSP treatment chemicals, including pre-treatment, and is ideal with lead-free solders. It is used with TAM 55 gold to produce the highest quality ENIG, with the highest yields, possible today.

TAM-55 advanced immersion gold bath minimizes nickel corrosion, optimizes gold distribution. A special additive minimizes nickel dissolution and thus leaves a robust nickel surface following the immersion gold reaction. TAM-55 protects and maintains the solderability of the electroless nickel in an ENIG deposit. It is ideally suited for use as a solderable finish for small SMT and BGA pads. For maximum compatibility, use Nimuden NPR Series electroless nickel as the underlying deposit for PWB and IC packaging. TAM-55 may be used for both ENIG and ENEPIG applications, allowing a single source immersion gold for plating lines where both finishes are employed.

Gobright® TAW-66 Immersion Gold provides superior performance, with low porosity and low nickel dissolution. It operates at 1 g/l gold metal, and offers high solder joint reliability, with minimal effect on the nickel layer.

Electroless Nickel, Electroless Palladium, Immersion Gold (ENEPIG)
ENEPIG is formed by the deposition of electroless nickel, followed by electroless palladium, with an immersion gold flash.  ENEPIG has exceptionally wide application: it is suitable for soldering, gold wire bonding, aluminum wire bonding, and contact resistance.

RoHS requirements, and increased focus on package reliability, have heightened interest in ENEPIG. ENEPIG performance is stellar in forming highly robust solder joints with lead-free SAC-type alloys.

In extended solder joint life testing (150°C for up to 1,000 hours), shear ball tests indicate no loss of solder joint strength. SEM studies and elemental analysis shows that the presence of palladium at the joint interface dramatically reduces inter-metallic (IMC) propagation, making ENEPIG the leading choice finish for packages that require soldering and wire bonding, with lead-free SAC type alloys.

The ENEPIG process is an excellent solution for IC package PCB substrates, particularly ceramic-based SiP products. Unlike electrolytic processes, ENEPIG carries no requirement for bussing lines, a factor which translates to additional flexibility in the design of circuits, and allows higher-density designs.

Finally, ENEPIG is immune to the "black pad" issue. Palladium is plated onto the electroless nickel via chemical reduction, as opposed to a displacement reaction, so there is no opportunity for compromise of the electroless nickel layer.

The ENEPIG process is less expensive than electrolytic or electroless  bondable gold.  Savings can easily reach 80% of the total final finishing cost when traditional electrolytic nickel gold processes are replaced with ENEPIG.

Talon for ENEPIG deposits an electroless / autocatalytic palladium for use as a surface finish for electronic and PCB applications. The palladium surface is both solderable and aluminum/gold wire bondable.

The bath has a low palladium metal content and is highly stable. The rate of deposition and quality of the deposit are exceptionally consistent throughout the bath life.

One version of UIC Talon allows palladium to be deposited directly on to copper, aluminum or electroless nickel. Talon is now the most popular electroless palladium for ENEPIG.

GoBright® TWX-40 gold electrolyte plates directly on electroless palladium depositions for ENEPIG processes, as well as optimized ENIG processes. The electrolyte deposits uniform gold films up to 0.3 µm independent of pad sizes and PCB surface potential.

Thanks to its semi-autocatalytic reaction, the Ni/Pd/Au film provides excellent wire bondability, and solderability using lead-free solder. Corrosive attack on the intermediate nickel layer is prevented. For optimum performance, use Uyemura electroless palladium baths as the underlayer for PWBs and IC packages.

Altarea® TPD-21 is an autocatalytic electroless palladium bath for surface mount applications, including those with fine pattern characteristics. This pure palladium bath has excellent wire bonding characteristics for PWBs and IC packages, and excellent solderability using lead-free solder. As-plated hardness is 280Hv.

The bath is exceptionally stable and easy to control. For optimum performance, use Nimuden® NPR series as the electroless nickel bath under-layer.

KAT UF (ENEPIG) Universal Finish
This unique Ni/Pd/Au surface finish is solderable, aluminum and gold wire bondable, and a superb contact surface. The recommended thickness is 3 – 5 microns (120 – 200 µins) of electroless nickel, 0.16 micron (4 – 6 µins) of electroless palladium, and 0.02 to 0.04 micron (1 – 2 µins) of immersion gold.

ENEPIG exhibits the highest degree of solder joint reliability of all available finishes with lead-free SAC 305 alloy. The palladium slows the diffusion of Sn into the Ni, resulting in a minimum thickening of the nickel/tin IMC, even following 1000 hours at 150°C.

Note: ENEPIG isn't the first choice for Sn/Pb eutectic solder. The palladium does not form intermetallics with Pb, and this results in a disrupted IMC layer that may compromise the reliability of the solder joint. MORE

KAT SP ENIG for Selective Plating
This modified KAT ENIG process accommodates the processing needed for the selective plating of ENIG and OSP (organic solderability preservative). The nickel bath is sulfur-free and more corrosion resistant. The gold is a much tighter, lower porosity gold coating.

KAT GW Electroless Nickel with Electroless Gold for Gold Wire Bonding
In this process, the standard ENIG deposit is followed by an electroless gold step. Here the gold thickness is built up to meet the requirements of gold wire bonding.

Gobright-TMX is a neutral pH electroless gold. AuBEL is an alkaline pH electroless gold process.


Electroless Palladium, Immersion Gold (EPIG)
EPIG nickel-free PCB finish is gold wire bondable, solderable, and ideal for HF use. It has opened up a wide, new design avenue for high frequency applications and designs with reduced spacing.

The EPIG process deposits palladium directly onto copper. Eliminating the nickel means there’s less build-up on circuits, and circuits can be controlled with smaller geometries. It’s a perfect fit for applications that demand smaller features and better clearances.

EPIG offers unique and significant advantages for microwave applications, flex circuits, and end users requiring high purity levels. These advantages include:

  • No nickel to fracture on bending for flex circuits
  • Maintains solderability and wire bondability to copper circuits
  • Short process time
  • No EN to pose corrosion issues
  • No skin effect on low current, HF applications
  • Non-magnetic
  • Suitable for tight lines and spaces
  • Easy to visually inspect
  • Reworkable in most circumstances

ENAG Electroless Nickel / Autocatalytic Gold

ENAG is a high-performing final finish for wire bondable deposits, and an excellent alternative to immersion chemistry, or ENEPIG. Deposits 120-240 μins of nickel, 8-40 uins of electroless gold. Read "Neutral Auto-Catalytic Electroless Gold Plating Process" in the Uyemura library.

PRESA RGA-14 Immersion Silver (View Animation Clip)
The requirements of newer electronic parts have caused PCBs to evolve and demand improved manufacturing methods. One important requirement is high-density mounting. HASL exhibits poor thickness distribution and cannot meet the needs of high-density mounting.

The emphasis on environmentally favored products has also advanced the cause of eliminating lead. OSP's formulations are not capable of preventing copper oxidation under the higher-temperature assembly conditions associated with lead-free. Uyemura's RGA Immersion Silver was developed to meet those challenges.

Immersion silver is a simple process, with silver directly displacing copper in an immersion reaction. RGA-14 is a high productivity process, compatible with horizontal conveyorized equipment.

The RGA Immersion Silver deposit is uniform and meets thickness distribution criteria. It provides an ideal soldering surface under eutectic and lead-free assembly temperatures, and, with proper packaging and storage conditions, has an excellent shelf life.

Plating Bath
The Immersion Silver plating bath is very stable because the reaction is displacement-type. It does not decompose with UV light, and, because it is a low temperature process, will not attack the substrate or soldermask. The immersion silver deposits only on copper, and not on other areas (such as can be seen with auto-catalytic baths).

PRESA RMK-25 Immersion Tin for PWB and PKG
The Presa RMK-25 immersion tin bath produces a highly uniform surface finish (thickness control is 1.5 standard deviation from the mean) that is ideal for backplane and other press fit applications. The flat microstructure has excellent aesthetics, and minimal copper etchback. Solderability is excellent, even with high temperature solders and when subjected to lengthy storage. The finish is compatible with both eutectic and lead-free solder.

Tin is deposited only on the copper surface, via displacement; process cycles are up to 3X faster than the competitive average. Deposits are highly consistent throughout the life of the bath. The RMK-25 solution has a relatively low operating temperature, is fluoride-free, and can be used with vertical or horizontal equipment.

RMK-25 is a highly differentiated immersion tin that combines ionic cleanliness, excellent appearance, exceptional uniformity, and processing speed that can triple both line capacity and productivity.

RMK-25, Uyemura's highly successful immersion tin, is designed to meet the robust requirements in shelf life, solderability and thickness uniformity for "Category 3 Coating Durability" per IPC Tin Specification 4554.

DIG Direct Immersion Gold on Copper
Uyemura's  Direct Immersion Gold process deposits a thin coating of immersion gold directly on the copper substrate. It is the best choice for a solderable surface, eliminating the shortcomings of other finishes.

It is ideally suited for "lead free" higher temperature assembly conditions. The gold coating is 1-2 micro inches (0.02– 0.05 microns). DIG is in direct competition with OSP finishes.

TCU-36 and TCU-41 are two versions of this process that can be custom tailored to meet specific manufacturing needs. Read the article, "Solder Joint Reliability of Gold Surface Finishes for PWB Assembled with Lead Free SAC Alloy" in the Uyemura library.


Electrolytic Nickel Gold
Uyemura offers a broad range of electrolytic nickel processes; sulfate, sulfamate and "high throw" electrolytic nickel. "Thru-Nic" electrolytic gold processes are available for hard or soft gold, depending on customer requirements.


Anodes for Gold Plating
Uyemura offers top of the line platinized titanium anodes for gold plating. The platinum is deposited from a molten bath that avoids micro-pores and micro-cracks found in traditionally produced anodes.


Stripping Solutions
Copkia Rip II Gold Stripper works at room temperature to remove plated gold from parts.

Copkia Rip Palladium Additive, added to the above product, turns the stripper into the highest performing palladium stripper.

PRESA RGA-SS-M5 Silver Stripper works at room temperature to remove immersion silver from PWBs.

RSS Silver Stripper strips immersion silver from printed circuit boards at room temperature. It is a hydrogen peroxide-based, cyanide-free bath that is effective even in the presence of an anti-tarnish overcoat. Important process advantages include a short dwell time, easy bath control, and a bath life of up to 3 months. RSS has three proprietary components.

Uyemura PCB finishes lead the world in plating performance. Products include final finishes, acid copper DC electroplate, ENIG, gold wire bonding, electrolytic nickel gold, immersion silver and immersion tin. Also, Electrolytic Palladium, and Copper Gobbler.


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