Polyetherimide adhesive

AppHcation of an adhesion-promoting paint before metal spraying improves the coating. Color-coded paints, which indicate compatibiHty with specific plastics, can be appHed at 20 times the rate of grit blasting, typically at 0.025-mm dry film thickness. The main test and control method is cross-hatch adhesion. Among the most common plastics coated with such paints are polycarbonate, poly(phenylene ether), polystyrene, ABS, poly(vinyl chloride), polyethylene, polyester, and polyetherimide. 

Adhesion studies of epoxy resins modified with high modulus and high glass transition temperature thermoplastics have shown adhesion can reach or even exceed that of the unmodified resin. The use of flexible polyamides or flexible epoxides resulted in shear strength increases in epoxy systems employed by Cunliffe et al. [144],polyethersulfones [18,145],polyetherimides [109,146,147], and polyetherketones [148-150]. 

Parts molded from polyetherimide can be assembled with all common thermoplastic assembly methods. Adhesives that are recommended include epoxy, urethane, and cyanoacrylate. However, service temperature must be taken into consideration in choosing an adhesive because PEI parts are generally used for high-temperature applications. Good adhesion can be effected by simple solvent wipe, but surface treatment by corona discharge, flame treatment, or chromic acid etch will provide the highest bond strengths. 

Good adhesion of metal to polyetherimide can be achieved where the polyetherimide is treated with KOH in ethanol. The depth of modification is in the um range. D. Foust presented at the International Symposium on Metallization of Polymers, Montreal, Canada, 1989. 

Polyetherimide Surfaces Chemically Treated To Improve Adhesion to Electroless Copper... 

Table I. Comparison of Polyetherimide Properties Following Adhesion Treatment...

Table IV. Adhesion Promoting Agents for Polyetherimide (ULTEM 2312)...

Polyetherimide A wide variety of commercially available adhesives can be used in bonding polyetherimide to itself or to dissimilar materials. Among these are polyurethane [(cure at RT to 302°F (150°C)], RTV silicones, hot melts (polyamide types) curing at 401 C (205°C) and epoxies (non-amine type, two-part) (12). 

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. 

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. ... 

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. ... 

An overview of the chemical methods employed to pretreat the polyetherimide is outlined in Figure 1. Removal of 0.5 )im of the polymer surface was accomplished via brief, 0.5 minute, contact with concentrated sulfuric acid. The subsequent water rinse resulted in the formation of a white film or residue. This layer could be removed either through solubilization or oxidation. Utilization of a solubilizer for the debris removal step also required a separate adhesion promotion step. The Standard 2312 process described previouslyS. 10,11 js solubilizer-free and depends on oxidation of the white residue to effect its removal. In this case, no separate adhesion promotion step is necessary and chemical modification of the polymer occurs in each of the principal pretreatment steps. ... 

During the electroless metallization of unfilled polyetherimide plaques or films it was observed that metal/polymer delamination, i.e., blistering, occurred whenever both sides of the sample were plated simultaneously. Metal/polymer delamination was detected irrespective of whether the Standard 2312 or adhesion promoter-based pretreatment system was employed, or the choice of metal. 

Previous studies have shown that 18 g/mm of mechanical adhesion is required to avoid delamination during electroless plating. Pretreatment of unfilled polyetherimide by the standard processes produced <9 g/mm of mechanical adhesion O. Therefore, the mechanical adhesion component by itself is not sufficient to maintain intimate contact between the metal and polymer layers. This accounts for the observed blistering. 

Table II. Effect Of Substrate Thickness On The Adhesion Of Copper To Unfilled Polyetherimide. ...

The overall scheme employed to pretreat unfilled polyetherimide substrates utilizing nitric acid as the impiegnator is given in Table IV. Unfilled polyetherimide substrates could be plated on all sides without delamination when this pretreatment scheme was employed. Furthermore, excellent adhesion was obtained for either an initial copper or nickel coating. Table V. Application of cathodic charging techniques to impregnator-pretreated polyetherimide... 

Table V. Adhesion Of Electrolessly-Deposited Metals To Unfilled Polyetherimide Substrates. ...

Table XI. Copper Adhesion to Polyetherimide Film Following Simulated Soldering Conditions.

Table XII. Effect of Filler Loading on Adhesion of Copper to Glass-filled Polyetherimide Pretreated by the Standard 2312 Process.

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 ... 

Contact of copper-metallized polyetherimide widi dilute acid solutions resulted in undercut and adhesion loss. Figure 2 demonstrates that the amount of undercut increased widi dwell time in 10 v/v% sulfuric acid solutions. The adhesion loss was related to the degree of undercut observed (vide infra). Hgure 3 presents the effects of pH and temperature on undercut for copper. It was found that both strong acids and bases could affect the metal lyiiKr bond. This is in accordance with the amphoteric nature of copper (vide supra). Moreover, temperature could greatly accelerate the undercut rate. 

Table I. Effect of Chemical Agents on the Adhesion of Evaporated Copper to Polyetherimide Film.

Atomic hydrogen may also play a role in die observed adhesion loss of polyetherimide films electrolessly metallized with copper or nickel (Note this adhesion loss may be obviated by increasing the mechanical adhesion component by altering the pretreatment methodology ). Molecular hydrogen is formed during the metal deposition reactions, equations 8 and 9. The mechanism by which... 

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