Plating on Polyetherimide
Q. I recently received a request to plate gold on a material called Ultem. What is the composition of this plastic, and what is the best method for plating it with gold? P.K.
A. Ultem is a member of the polyetherimide (PEI) family of thermoplastic resins. It was originally developed by General Electric, but now is produced by an offshore chemical company. PEI is chemically resistant, so special processes have been developed for metallizing this material. One of the classic ways is to use what is sometimes called the well and etch technique. In this process, an organic solvent is used to make the polymer surface swollen, and then it is etched using chromic acid or a chromic acid-like material. This type of treatment modifies the surface so that other coatings can adhere to it. There also are other proprietary methods that have been developed to minimize the surface modification. The key here is to create a surface that metal will adhere to.
Metallizing the surface of PEI materials is usually done with proprietary chemicals that are available from vendors that specialize in this type of plating. The first step is to deposit a copper layer on the surface of the plastic. Then you can deposit non-copper layers. The exact procedures must be worked out for each type of PEI. It helps to have good cooperation between the company that manufactures the plastic parts and the company that does the metallizing.
Keep two things in mind:
1. Do not attempt to “reinvent the wheel.” Use chemicals that have been commercially developed for this process. Trying to formulate “home brews” wastes a lot of time and energy.
2. Find a chemical vendor that specializes in this type of metallization, and work with it to develop your process.
An older book on this subject, Metallizing of Plastics—A Handbook of Theory and Practice by Richard Suchentrunk, is out of print but is available from Amazon.com.