What is the ENEPIG process in PCB industry? What are the advantages of ENEPIG?

                                 What is the ENEPIG process in PCB industry? What are the advantages of ENEPIG?

Electronic products tend to be thinner, smaller, lighter, and include more features and high speeds. As a result, the electronics packaging industry has developed a variety of advanced packaging technologies and methods that enable the density, number and variety of integrated circuit (IC) to be added to the same PCB. Increasing package and connection density has driven the evolution of packaging methods from through-hole technology (THT) to surface mount technology (SMT), which has led to a further application of wire bonding. The reduced cable spacing and application chip size packaging technology (CSP) increase the density of the device. At present, the commonly used surface treatments such as OSP, HASL, Immersion Tin, Immersion Silver, ENIG etc. can not meet all the needs of the lead-free assembly process, so we will describe an ENEPIG surface treatment process for integrated circuits.

ENEPIG that is Electroless Nickel Electroless Palladium Immersion Gold, it deposits a layer of palladium between the nickel layer and the gold layer to prevent mutual migration between nickel and gold without the appearance of black pads.

1. The advantages of ENEPIG are as follows:

1). The gold plating is very thin,  it can be used to make gold wire or aluminum wire;

2). The palladium layer separates the nickel layer from the gold layer to prevent mutual migration between gold and nickel; no black nickel phenomenon occurs;

3). Improved solderability after high temperature aging and high humidity, excellent solderability, and good solderability after high temperature aging;

4). The cost is lower, the thickness of gold is 0.03~0.04um, and the average palladium thickness is about 0.025~0.03um;

5). The palladium layer is thin and uniform;

6). The nickel layer is lead-free;

7). The coating has good compatibility with solder paste;

8). Ideal for SSOP, TSOP, QFP, TQFP, PBGA and other package components;

2. Detailed description of ENEPIG process:

1) For ENIG's bonding PCB, the gold layer thickness is required to be thicker than 0.3 microns, but the ENEPIG PCB can be satisfied with only 0.1 micron palladium and 0.1 micron gold. Palladium is a much harder metal than gold. The reasons for addding the palladium layer are that the corrosion of pure gold and nickel is serious and the welding reliability is poor and Palladium also has a role in thermal diffusion, so ENEPIG is more reliable than ENIG.

2) ENEPIG process has been developed for many years, but there are not many mass production factory in China. The process of ENEPIG is basically similar to the ENIG process. The production process is: degreasing - microetching - pickling - prepreg - activation of palladium - chemical nickel (reduction) - chemical palladium (reduction) - chemical gold (replacement).

3) ENIG currently has a lot of black nickel problems. Adding a layer of palladium between the nickel layer and the gold layer can effectively prevent black nickel and the diffusion of Nickel.

4) ENEPIG surface treatment was first proposed by INTER. Now it is often used in PCBs with BGA design. This kind of PCB needs bonding gold wire on one side and welding on the other side. The thickness of the gold layer is different for both side. The gold thickness of the bonding side needs to be thicker, about 0.3 micron or more, and the solder side only needs about 0.05 micron. Therefore, the ENEPIG production requires special control of the thickness of the gold layer thickness on both sides.

Companies that are currently applying this process are: Microsoft, Apple and Intel , etc.