Copper foil Treatments

Flexible copper-clad laminates with nonthermoplastic polyimides were prepared in a two-step process entailing isolating the polyamic acid and then thermally imidizing to the corresponding polyimide. Plasma or thermal treatments of selected polyimides generated materials with excellent bonding strength when evaluated on laminated copper foil. 

Bonding strengths of experimental agents were evaluated on laminated copper foil after samples were subjected to plasma treatment or after being heated to 380°C. Testing results are provided in Table 2. 

Subsequent to the manufacturing of the base copper foil, a variety of surface treatments are typichlly apphed, and these too will vary depending on the usage environments. These treatments faU into four categories. 

Brist, Gary, Hall, Stephen, Clauser, Sidney, and Liang, Tao, Non-Classical Conductor Losses Due to Copper Foil Roughness and Treatment, ECWC10/IPC/APEX Conference, February 2005. 

In this laser direct drilling method, copper foil is etched down to about 5 pm and its surface goes through oxide treatments such as black oxide or other methods, typically as alternatives to oxide treatment, which is normally an etching process. The copper thickness is further reduced by 1 pm, and the surface color becomes dark, allowing the CO2 beam to penetrate. 

Epoxy does not adhere well to untreated copper surfaces.This means that some type of treatment must be applied to the innerlayer before lamination. One option is to use double-treated copper, discussed earlier. Double-treated copper has a rough surface with a treatment supplied by the material vendor. Many ML-PWB fabricators report excellent results with double-treated copper. Others report problems with contamination and difficulty with rework. The alternative to using pretreated copper foil is to use a chemical treatment after etching. 

Carbon Suspensions. Black Hole, the second direct metallization techniqne, was patented by Dr. Carl Minten in 1988 and pioneered by Olin Hnnt, who sold their technology to MacDermid in 1991. MacDermid improved the process considerably and called it Black Hole II. Instead of palladium activator. Black Hole II uses carbon suspensions as its conductive medium. Polyelectrolyte conditioned nonconductive surfaces absorb carbon sites, and they line up after heating. To ensure sufficient conductivity, the carbon treatment is performed twice. Residues of carbon sites must be removed from the copper foil surface by a... 

Waste disposal. Spent or by-produd etchant is usuahy sent off-site for copper reclamation. There is usually a fee for this service depending on copper content and distance to the reclamation fadhty. The solutions must be free of unreacted oxidizer (see previous chlorate system discussion). Etchant can contain traces of zinc, chromium, and arsenic from the foil treatments. 

The manufacturing process is illnstrated in Rg. 61.4. Mostly, these films are processed and supplied in roll form. The snrfaces of polyester films and polyimide films undergo special processes such as sandblasting and plasma treatment to achieve a rehable bond strength. A specially blended adhesive resin is coated on the film and dried. Then a copper foil is laminated continuously under appropriate temperature and pressure.The surfaces of the copper foils receive a specific treatment according to the requirements of each laminate s manufacturer. 

The carbon dioxide laser has greater productivity than the excimer laser or the UVYAG laser when used to generate via holes larger than 60 /rni in diameter however, it cannot drill through copper foil directly. As a result, a black surface treatment is required on the thin copper foils before the laser operation. (See Fig. 63.6) Comparisons of the technical capabihties of these micro via processes of the laser systems are shown in Table 63.4. 

One of the better surface treatments for copper, utilizing a commercial product named Ebonol C (Enthane, Inc. New Haven, CT), does not remove the oxide layer but creates a deeper and stronger oxide formation. This process, called black oxide, is commonly used when bonding requires elevated temperatures for example, laminating copper foil. Chromate conversion coatings are also nsed for high strength copper joints. 

Soluble LCP (sLCP) was supplied by Sumitomo Chemical Co., Ltd. (Tokyo, Japan) (Okamoto et al. 2005, 2006). The sLCP was dissolved in n-methylpyrrolidone. A LCP film was obtained from sLCP by a solvent casting method described as follows The sLCP was applied to a substrate such as copper foil by bar coating and subjected to heat treatment at 100 °C for 1 h. The sLCP film was in an amorphous (non-crystalline) state and therefore transparent. The film was heated to 300 °C for 3 h under nitrogen atmosphere, and then the liquid crystal phase in the film was reached. After that, the film turned semitransparent or opaque. 

MeV a-particles and used the Au/Ir source after annealing without any further chemical or physical treatment. Commercially available sources are produced via Pt(p, n) Au. The most popular source matrix into which Au is diffused is platinum metal although it has the disadvantage of being a resonant matrix - natural platinum contains 33.6% of Pt. Using copper and iridium foils as host matrices for the Au parent nuclide, Buym et al. [327] observed natural line widths and reasonable resonance absorption of a few percent at 4.2 K. 

Fig. 18. Mossbauer spectra of Cr-Fc304 catalyst after room temperature exposure to air and COz/CO treatment at 703 K. (a) Spectrum in air at 296 K after sample has been stored in air. (b) Sample from (a) reduced in a C02/CO = 4 mixture at 703 K for 10 hr. Spectrum obtained in reaction mixture at 703 K. (c) After cooling (b) to 483 K. (d) After cooling (c) to 296 K. (e) Spectrum of a 0.001-in. Fe NBS standard foil at 296 K. Zero velocity is with respect to a 7Co in copper source. Reproduced from Tops0e and Boudart (96) with permission.

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