Choosing the Right Thin Film Metallization

Feb 14, 2014

The metallization that you select for your next thin film design is critical to the success of that product. The metallization scheme is defined as the metal layers that make up the lines and features on a thin film circuit or interconnect. A typical metallization scheme consists of an adhesive layer, a solder layer, and a conductor layer.  If a design includes integrated resistors, then the adhesive layer serves double duty as a controlled resistive layer and the adhesive layer. The metallization scheme obviously plays a huge role in electrical or optical device performance, providing component and die to substrate connections, and substrate to package connections. Most people don’t realize it, but the metallization scheme actually needs to meet a surprisingly long list of performance requirements, depending on the application:

  1. Electrical Conductivity
  2. Thermal Conductivity
  3. Solderability
  4. Wire Bondability
  5. Epoxy Adhesion
  6. Reliability (tape test, shock, vibration, thermal, die shear)
  7. Corrosion Resistance
  8. Optical Flatness
  9. Compatibility with lead free SAC-type solder alloys for RoHS compliance
  10. Power Handling
  11. Cost
  12. Minimum line & space resolution
  13. Reworkable (multiple cycles)
  14. Maximum Service Temperature (high and low)
  15. Ability to integrate with holes, filled vias, resistors, capacitors, solder dams, cross-overs, etc.

The elimination of lead from electronic devices as mandated by RoHS (Restriction of Hazardous Substance) is changing the playing field for many global manufacturers. This is driving a transition among many customers from Nickel to Palladium as a SAC compatible solder layer (SAC = SnAgCu or Tin/Silver/Copper). The SAC alloys have become the prevailing solder alloy to replace tin-lead solders.

Many of our customers have not yet discovered the virtues of Palladium versus Nickel as a solder layer. Palladium (1 x 107 S/m) is slightly less electrically conductive than Nickel (1.4 x 107 S/m) but it is still well suited for high frequency applications. Palladium also causes much fewer solder problems (from Ni-Au diffusion) than Nickel.

Unfortunately, there isn’t one single metallization that “is a one size fits all” yet. A metallization scheme really must be custom designed and optimized based on your specific product application. At UltraSource, we can offer you many different metallization schemes for your next design, depending on whether you need low cost or high reliability, Pb/Sn solderability or Lead-Free solderability, low power or high power. We can supply low cost, high volume products and we can also supply Hi-Rel Class K products. We stand by ready to assist you in making a wise choice for the metallization scheme on your next thin film design and to manufacture your devices.

If you need your circuits in days instead of weeks or months, don’t forget to ask about our UltraFAST Rapid Prototyping program.

2017-02-15T20:40:03-05:00February 14th, 2014|News|0 Comments

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