Thick-film copper

Thick-film copper metallization is typically selected for the low cost of the conductor inks in comparison to gold inks. Other fhick-film conductor inks, such as silver and palladium silver, are also used when low material cost is... 

The firing process for thick-film copper is different from tirat of otirer thick-film conductors. Because copper readily oxidizes in tire presence of oxygen, the standard thick-film firing process must be modified to prevent tire oxidization. Instead of air flowing through the furnace, dry nitrogen with less than 10 ppm of oxygen is used [5]. 

Thick-film copper conductor inks are not pure copper. The ink consists of a functional material of copper, a solvent, a temporary binder, and a permanent binder. The permanent binder tailors the CTE to that of the substrate. It also aids in the adhesion of either the substrate or the dielectric. The thick-film firing process in nitrogen bums out the solvent and temporary binders. This leaves just the copper and the permanent binder. In addition to tailoring the CTE, the permanent binder significantly reduces both the electrical and thermal conductivities of the conductor. A typical fired conductor thickness is 15-18 pm. If it were pure copper, it would have a sheet resistivity of 0.94-1.13 mQ/Q. The 9924 thick-film copper conductor material from El DuPont Electronics specifies a sheet resistivity of 1.9-4.8 mD/ for the same thickness. This results in the published resistivity of this thick-film material being only 23% of the resistivity of pure copper. 

Screen printing — thick-film copper process flow for two conductor layers. 

Assume that the thermal conductivity of the thick-film copper is 20% of pure copper. 

For substrates metallized with thick-film copper that will see subsequent soldering, manufacturers typically plate them with nickel and optionally with a top layer of gold. Some manufacturers will solder dip their copper thick-film subsfrafes after nickel plating. The resulting metallization has toe same solderability and wire bondability characteristics as DEC and plated copper. 

V. P. Suita and R. J. Bacher, Firing Process-Related Failure Mechanisms in Thick Film Copper Multilayers, Proc. 36th Elec. Comp. Conf, Seattle, pp. 471 80, 1986. 

R. Gardner et al., Materials Science Aspect of a Thick Film Copper/Dielectric System, Proc. Inti. Symp. Microelec., pp. 285-294,1990. 

Fig 3. Predicted electro-acoustic response for PVDF film bonded to aluminium and backed with different thicknesses of copper. (Thicknesses shown in pm.)... 

Figure 7 shows a plot of T versus u for a monolayer and a five layer thick film of CU2O on copper in the region of the strong lattice absorption of CupO.-S- Two features should be noted. 

The crosslinked ViSi (OCH,), silicone type substrates were spread with a microslide on a mechanically polished copper sample to form several tens of pm thick films. Then, they are transferred into the spectrometer chamber without passing through the atmosphere. 

A 1-mm thick copper substrate was coated with a 200 -pm thick film consisting of the Step 3 product and then dried at 50°C. The film was coated with 200 pm of the Step 2 product (10 mg) dispersed in 100 ml of ethanol. Thereafter the coating was dried at 70°C, and the product was isolated having MWNTs aligned perpendicularly to the copper substrate at regular intervals. 

The electrochemistry of copper anodes in neutral and alkaline media has been studied in detail [223-226]. This complicated process includes, as a rule, the growth of ultrathin (several nanometers thick) films of CU2O, CuO, and also mixed and non-stoichiometric oxides. Until recently, it was assumed that cations do not affect the dissolution and passivation of copper. However, the first attempts to synthesize HTSCs and (or) their precursors showed that copper oxide films, formed when the potential of a copper electrode is cycled in a Ba(OH)2 solution, incorporate substantial amounts of barium [227]. This result was subsequently confirmed not only for potentiodynamic [228] but also for potentiostatic [229] oxidation modes. It has been suggested that Ba[Cu(OH)4] or Ba[Cu2(OH)6] forms in the supersaturated nearelectrode layer [229]. Similar studies with other alkaline-earth cations at high pH are difficult to conduct due to the poor solubility of the corresponding hydroxides. 

Figure 10.2 ATR-FT-IR images of a copper grid with a thick film of PDMS pressed behind and measured using (a) the ordinary and (b) the new imaging diamond ATR accessory (c) the white light image of the copper grid measured with a 5x objective.

The hot stage has not only been applied to optical and atomic force microscopes, but also to scanning electron microscopes. Hot-stage accessories are available on environmental SEMs that can collect ESEM images at elevated temperatures. Applications to the electronics industry include fluxless soldering, intermetallic growth studies, and copper thick-film sintering studies (92-94). 

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