PWB Processes: ENEPIG


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.

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.

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.