Metal-polyetherimide chemical bond

To function as a circuit board, the polymer must be metallized. A key aspect of this technology pertains to the adhesion developed and maintained between the metal and polyetherimide. The adhesion between a metal and a ooivmer can be viewed in terms of ohysical or mechanical adhesion, and chemical adhesion. Mechanical adhesion results from interlocking of the metal and polymer phases due to die creation of re-entrant cavities or macroscopic fissures in the polymer structure. Mechanical adhesion may also result from the presence of fine, shallow pits along the polymer surface. Chemical a esion relates to the formation of chemical bonds between the metal and polymer layers. The chemical interactions can result from actual charge transfer, e.g., ionic or covalent bond formation, van der Waals forces, or electrostatic or acid-base interactions. ... 

The reactions of various chemicals with the metal/polymer bond were examined utilizing samples of 125 pm thick polyetherimide film which had been metallized on only one side. Traces, 3.2 mm wide, were created similarly to those employed for peel test measurements. The fibn is translucent and thus the degree to which the metal/polymer interface was altered could be viewed dirough the back (dorsal side) of the substrate. The normal appearance of the metal/polyetherimide interface, after heat treatment, is bronze. A color change from bronze to pink was observed at the interface when reactions between the... 

The outer portions of the underside of the metal trace become bronze colored. As the bond formation interaction progresses across the entire metal strip, a uniform bronze hue is achieved. In region B the metal/polymer adhesion is developed completely and no deleterious effects are observed. During this stage, adhesion at the metal lymer interface is predominately due to oxygen-aided chemical bonding between copper and polyetherimide l A Finally, in region C, overoxidation or thermal destruction of the chemical portion of the... 

An aqueous chemical pretreatment for unfilled polyetherimide substrates is described. The process includes the use of a chemical impregnator to increase the mechanical adhesion component and avoid metal lymer delamination during the initial electroless metallization step. Excellent adhesion was achieved for copper or nickel to both injection-molded plaques and extruded films. The metalA>olymer bond was found to be durable in thermal environments (dry and moist) as well as in simulated solder tests. Failure occurred within the polymer substrate during 90° peel testing. The process was found to be applicable to filled substrates as welt. 

Recent advancements have yielded methodologies for chemically pretreating the polyetherimide surface thereby introducing a chemical component to the metal olymer bond b. These schemes were both nonaqueous and aqueous. FmthennoFe, the methods employed an adhesion promoter or else relied on chemical modiHcation of the polymer. ... 

Research activities within our laboratory have focused upon pretreatment methodologies, electroless or vacuum metallization , and the thermal durability of the bond formed between copper or nickel and polyetherimide D. These studies have demonstrated that excellent, >150 g/mm, adhesion could be obtained and maintained between metals and various polyetherimide substrates. Further, the copper/polyetherimide bond° is predominantly chemical in nature ... 

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