Copper Thickness

This type of coil was prepared from copper cladded printed circuit board material by applying photolithographic techniques. The p.c. board material is available with difierent copper thicknesses and with either a stiff or a flexible carrier. The flexible material offers the opportunity to adapt the planar coil to a curved three dimensional test object. In our turbine blade application this is a major advantage. The thickness of the copper layer was chosen to be 17 pm The period of the coil was 100 pm The coils were patterned by wet etching, A major advantage of this approach is the parallel processing with narrow tolerances, resulting in many identical Eddy current probes. An example of such a probe is shown in fig. 10. 

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

The so-called 1-oz board in the USA is actually equivalent to 1.4 mils (35 tm) copper thickness. Similarly the 2-oz board is twice that. For a moderate temperature rise (less than 30°C) and currents less than 5A, we can use a minimum llmils width of copper per amp for 1-oz board, and at least 7mils width of copper per amp for a 2-oz board. This rule of thumb is based on the DC resistance of the trace only. So to decrease its inductive impedance and AC resistance, higher trace widths may be required. 

FIGURE 7.23 The overall average overburden copper thickness and step height of 100 pm copper in the 50 % metal density region on a SEMATECH 854 patterned wafer (from Ref. 109). 

Conventional CMP typically requires an overburden of copper of at least 4000 A due to low planarization efficiency. An overburden of 1000 A is sufficient for ECMP to achieve planarization without compromising performance in terms of dishing, erosion, and defectivity. A stress migration test was carried out at 250 °C for 333 h on a structure with metal level 1 and level 2 lines with thickness in the range of 0.14-0.16 pm. An increase in resistance by more than 10% is considered a fail. The reduction in electroplated copper thickness can reduce the number of fails in stress migration test as shown in Table 11.1. 

TABLE 11.1 Stress Migration Fails as a Function of Electroplated Copper Thickness. 

Unpattemed electroplated copper wafers were polished using an IPEC 472 polisher equipped with an IR temperature sensor which measures pad surface temperature. The copper rate was determined from copper thickness measurements from a Tencor RS55 resistance monitor, calibrated to cross-sectional SEM micrographs. The SEM tools are regularly calibrated to national standards. 

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). 

Therefore, we have to ensure that our DM choke does not saturate with a peak instantaneous current of 8 A. Both the CM and DM chokes must have copper thick enough to handle 1.3 ARMS. 

Clearly, the no-acid electrolyte significantly improves the copper thickness uniformity which in turn leads to better process integration with subsequent CMP steps. 

Plated Copper Thickness (A) Resistance ( ) Tape Test... 

Ratio I Comer thickness to trench/via copper thickness,... 

IfoZr wire diameter, aoio. Copper Thickness 0.0005 on radius. 

In one instance, copper was electrolessly plated using a commercial bath (see Experimental, Bath C). The resulting hologram was very reflective and had exceptional definition. A transmission electron micrograph of the cross section is shown in Figure 2. The copper follows the contours of the hologram. The copper thickness is ca. 100 nm. 

The polyetherimide was treated according to the Standard 2312 process. Following the post-electroless heat-treatment step, the copper thickness was electrolytically increased, 3.2 mm wide traces created and a final heat treatment at 110°C performed for 16 hours. The peel strength vi as evaluated subsequent to this step. 

Etching. It involves removal of metals and dielectrics and may include both wet and dry processes. Copper can be etched with cupric chloride or other isotropic etchants, which limit the practical feature sizes to more than two times the copper thickness. The uniformity of etching is also critical for fine line feature circuits. New anisotropic etching solutions are being developed to extend the fine line capability. 

A copper thick-film conductor, 0.2 in. long and 0.01 in. wide, is fabricated using the standard screen-printing process and is shown in Figure 8.3. The ink manufacturer s data sheet specifies a resistivity of 1.9 to 4.8 mfl/Q for a 13-pm fired thickness [5]. Using the worst-case value of 4.8 mfl/Q, the resistance of the conductor is calculated using Equation 8.6. 

The width of etched copper conductors is a function of the copper thickness. A O.OlO-in.-wide conductor is one manufacturer s minimum when used with 0.005-in.-thick copper. For 0.012-in.-thick copper, the minimum line width increases to 0.0275 in. The spacing between etched conductors ranges... 

Thick-film ink manufacturers do not publish thermal conductivity data for their conductor and via-fill inks. Work by Harshbarger [16] and Krum [17] has shown that the thermal conductivity of thick-film conductor inks is approximately 20% of that of pure metals. A first-order approximation of the thermal conductivity of thick-film conductor inks is to multiply the percentage of the published value of electrical conductivity (the reciprocal of resistivity) of the ink and the thermal conductivity of the pure metal in the ink. For copper thick film, as described in the above example, the electrical... 

A chip whose effective area is 10 x 10 mm is soldered to a conductor of plated copper on thick film. Find the thermal resistance of the metalli2ation. The thick-film thickness is 10 pm. The plated copper thickness is 0.002 in. Converting the plated copper thickness to meters ... 

Although the percentage difference in the two calculations is rather significant, the overall thermal resistance in the copper thick-film can be considered negligible. If the thick-film ink were silver-based instead of copper-based, then the thermal resistance degradation would be considerably less. 

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