This blog explains why there are problems associated with ENIG use and how a new product on the market – ENIG-PremiumTM – solves these problems. Electroless Nickel Immersion Gold (ENIG) is now arguably the most used finish in the PCB industry, however it can have reliability problems such as black pad related failures and brittle solder joints. Here’s why:
The reliability of solder joints, which connect surface mount components to PCBs, is essential to improve robustness and reliability of electronic assemblies. The most important factor in solder joint reliability is the robustness of the solderable surface finish because it ensures the reliability of PCB-to-surface mount component connectivity at a solder joint, which is critical to a device’s optimum operation over time. A bad surface finish results in a bad solder joint. This issue may lead to electrical continuity failures and result in low-quality performance, and ultimately, product recalls, product performance failures and customer satisfaction issues.
Over the past few years, LiloTree has worked with several customers to identify the root cause of the field failures of their products. They were all associated with ENIG related issues, according to Kunal Shah, chief scientist at LiloTree which is based in the Seattle area. Currently available ENIG surface finishes are prone to failures associated with de-wetting of solder, Shah said, component fall-offs and overall malfunction of electronic assemblies.
The following is a Q&A with Shah, who along with his team, has been working with several OEMs/PCB manufacturers currently testing/qualifying/adopting ENIG-Premium. For more background information about ENIG-Premium, click on this link to read an introductory blog.
Here are the questions and answers that will help you understand the problems with ENIG and how ENIG-Premium solves them:
Why are there problems with ENIG?
Electroless Nickel Immersion Gold (ENIG) has two processes; deposition of electroless Ni (Ni-P) followed by an immersion gold process. The immersion gold deposition is the displacement process where nickel atoms are displaced by gold atoms. This displacement process is the main root-cause of both black pad defects (hyper-corrosion) and brittle solder joint failures.
Why does the displacement of nickel atoms by gold atoms cause black pad defects and brittle solder joint failures?
Displacement of nickel atoms by gold atoms creates a localized enrichment of phosphorous. These phosphorous rich areas are non-wettable to solder and tend to create electrical continuity failures. Areas of the surface mount pads tend to appear as black in color when uncontrolled displacement of nickel atoms has taken place; hence the term, “Black Pads.”
Also, when the solder reflow process (solder attachment) is conducted, the intermetallics (interface bonding between solder and surface finish/copper pad) are softer and contain voids due to the phosphorous rich region. Hence, when any mechanical stress condition is applied, failures occur within the intermetallics in a brittle manner. Hence, brittle solder joints failures.
How does ENIG-Premium solve these problems?
ENIG-Premium is designed to eliminate the displacement process of nickel atoms by gold atoms. This has made the surface finish (ENIG-Premium) corrosion resistant (no black pads) and with robust solder joints (no brittle solder joint failures).
ENIG-Premium offers 10 times higher corrosion resistance which leads to complete resolution of black pad defects. Also, the intermetallics at the solder joints with ENIG-Premium are designed to be robust hence brittle solder joint failures are prevented. The findings of robust solder joints have been validated by a third-party testing laboratory. Also, the chemistry of immersion gold, the integral part of the ENIG process, is cyanide free (eco-friendly) for ENIG-Premium whereas most conventional ENIG offerings have cyanide based chemistries.
ENIG-Premium provides improved quality and reliability of electronic assembly products so manufacturers avoid major product field-failures and the potential consequences. Plus, ENIG-Premium costs no more than ENIG so you get an eco-friendly solution at no extra cost.
There are several OEMs/PCB manufacturers currently testing/qualifying/adopting ENIG-Premium. Once we start getting feedback, we’ll share it with you.