PCB Plating for Chip on Board Assembly

COB wire bonding
Chip on Board Wirebonding

Selecting the right PCB plating for Chip on Board assembly is crucial. One of the most frequent questions we are asked at Majelac Technologies is how should my Printed Circuit Board be plated in order to ensure wire bond-ability. PCB Plating for Chip on Board Assembly must be planned in advance to ensure manufacturability of the device. This planning begins with design rules and selecting the wire bond method to be used. Common wire bond materials include aluminum or gold wire.

Aluminum Wedge Wire Bonding and ENIG Plating

One of the most common wire bond methods for COB assembly is aluminum wire bonding. For aluminum wire bonding to a PCB the plating can be a low cost method known as ENIG or Electroless Nickel with Immersion Gold. With ENIG plating a PCB with Copper traces is plated with a Nickel layer and then the nickel layer has a flash gold layer on top. The Flash Gold is a barrier layer to protect the Nickel from oxidation. The wire bonding connection is actually from the aluminum wire to the Nickel plating. The main advantage of this method is inexpensive plating and relatively easy wire bonding. The disadvantage is Aluminum wire bonding is less flexible than gold bonding and generally requires larger bond pad pitch compared to gold bonding.

Gold Ball Wire Bonding and soft gold plating

For Gold Ball Bonding to Printed Circuit Boards a thick layer of soft gold has traditionally been required. In this Case the copper traces on the PCB are plated with a nickel layer and then a soft gold layer measuring between 30 and 50 micro-inches. The gold is electroplated and when plated correctly  provides an excellent surface for wire bonding. This method has the advantage allowing for fine pitch gold ball bonding. The disadvantages are high cost and the thick gold layer can cause reliability problems with surface mounted components due to gold dissolution into the solder.

Gold Ball Wire Bonding with ENEPEG plating

In recent years Electroless Nickel, Electroless Palladium, Immersion Gold plating has been proven to be the best compromise between cost and manufacturability. This method of plating is known and ENEPIG and is common referred to as the universal plating method. It is called universal plating because it offers good wire bond ability and good solder ability. It is suitable for RoHS solders as well as Eutectic SnPb solder. The typical plating thickness is 100 to 150 micro inches of nickel followed by 4 – 10 micro inches of palladium followed by 1-2 micro inches of gold. ENEPIG is suitable for both Gold and Aluminum wire bonding however for Gold Bonding the plating process must be well controlled. At Majelac technologies we receive PCB’s from many vendors and wire bond ability varies greatly. One simple test is to try and attach a ball bump on the PCB trace and then do a shear test. If the ball comes of cleanly there is an issue. If the ball comes off and exposes the palladium layer there is an issue. If the ball leaves some residual gold wire behind we are confident the material will work with automatic ball bonding.

At Majelac for PCB plating with Chip on Board we recommend using ENEPIG as a preferred plating method. For more information about Majelac Technologies Chip On Board wire bonding services please click the link below:


Prototype Assembly with Open Cavity Packages

Open Cavity Packages
Open Cavity Packages

Open cavity packages have evolved to be the preferred solution for prototype and low volume assembly of integrated circuits. For many years ceramic packages were the default option for prototype assembly of new semiconductor products. This presented a challenge for the industry because, while this type of package allowed for rapid assembly of initial samples, it rarely would represent the final product, which was typically a plastic package. This gap was noted by both the vendors of prototype assemblies and by their customers, who were looking for package solutions that could more accurately represent the production package.  This requirement gave rise to new and interesting concepts, starting with opening a plastic package using etching in order to remove the existing integrated circuit. This process was nick-named “Scoop and Goop”, referring to the removal of the old IC, “Scoop” and followed by assembly of a new IC in that package and the filling with epoxy to cover the IC, or “Goop”. This was a good first step because it had the advantage of providing a package that was the exact match to the intended production package.  However, there was a significant disadvantage when it came to the ease to wirebond, as the methods used to remove the molded plastic material were traumatic to the bond fingers.

A new approach was needed – the Open Cavity Package. Over the last decade so called pre-molded plastic packages were designed in which the plastic is molded to a copper lead frame with an open cavity (Open Cavity Package). After molding the parts are typically gold plated but in some cases the lead frame is pre plated. These pre-plated lead frames often receive palladium plating. These new packages have become the ideal method for prototype assembly and, in some cases, low volume assembly. In the industry they are referred to as open cavity plastic packages. They offer rapid prototyping combined with closely matching specifications to the actual production package, satisfying the initial obstacle faced when doing prototype or low volume assembly.

At Majelac Technologies we assemble pre molded plastic packages with formats including QFN, SOIC, and QFP. We stock pin counts ranging from 8 pins to 100 pins.  We can assembly prototypes in these packages in as little as 4 hours. For a list of available packages please check this link:

For a list of available packages please check this link

We can be contacted at www.majelac.com