The following sections are for Internal Company use only
3.2 Substrate
Metalization
The basic metalization scheme for thin film substrates contains Titanium-Tungsten/Gold (Ti-
W/Au), with a Ti-Tungsten (Ti-W) adhesion layer. When thin film resistors are required, a
Tantalum Nitride (TaN)/Ti-W/Au metalization layer is used. The TaN is available standard
in 50 or 100 ohms/square sheet resistances. The gold layer is fully sputtered on or
electroplated for normal etch-back processing; for plate-up purposes, only a gold flash is
applied. For special brazing applications, a metalization with nickel between the TiW and
gold is available.
3.3
Etch-Back Design Guidelines
3.3.1
Application
Easy to process, compatible with current processing techniques, capable of etching lines
down to 2.0 mils and spaces down to .8 mils.
3.3.2 Description
Etch-back processing forms a pattern by selectively etching gold away from a substrate
through a photoresist mask layer. The desired gold pattern is protected by the photoresist
during the etch process. The gold traces formed are slightly smaller (by the etch factor) than
the photoresist trace. The thin-film resistors are formed in the same manner: gold is etched
away from the site where a resistor is desired. The photo-patterning and etching processes
used to form the resistors are performed after creating the gold conductor layer.
3.3.3
Design
Rules
1. All substrates should have an ID Logo or Part Number etched in with the substrate
pattern. The lines of the logo should be at least 2.0 mils in width after etching.
2. The thinnest line achievable is 2.0 mil after etching.
3. The narrowest gap achievable is 0.8 mils after etching.
4. All substrate metalization should be 2 mils from any substrate edge to be cut.
5. Design the resistors to be at value after etching and when the sheet resistance of 50 ohms
or 100 ohms per square is reached. (Other resistivities per Table 2 and 3 are also
available.)
6. When a resistor value is unable to be measured directly, design in a test resistor of the
same size and value to be used on that substrate, or design a square test resistor having a
value equal to that of the sheet resistance (50 or 100 ohms typically).
7. The minimum size for the gold pads on either side of a resistor should be 4 mils by 4
mils. This will allow the resistor to be probed without being damaged.
8. Include the etch factor in both the L and W direction of the resistors
(see Fig. 2 on the following page). To make the etch masks
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