Electroless UBM Formation Process

　UBM is an abbreviation for Under Bump Metal or Under Barrier Metal. It is a film formed to ensure the reliability of bonding between metal pads on semiconductor chips and solder or wire bonding. From the perspective of barrier properties and surface protection during bonding, it is formed with a composition of nickel/gold or nickel/palladium/gold.

　Meltplate UBM process is a process to form UBM by electroless plating. Compared to the electrolysis bump forming process, the Melplate UBM process does not require exposure and development processes and can form UBM in a short time.
　In addition, Melplate UBM process includes patented technology in the pre-treatment and can be used for various types of aluminum electrodes, minimizing damage to the electrode and forming a smooth film. We can provide plating solutions to form Ni/Au or Ni/Pd/Au films according to your needs.　

　Melplate NI-869 is an electroless nickel plating solution for UBM.

• ・Deposition rate: 12 to 17 μm/hr
• ・Phosphorus content: 6 to 8 wt%
• ・Alkali metal, halogen and Pb free
• ・Excellent film formation even on micro electrodes with a diameter of 10 μm
• ・Excellent barrier property against Pb-free solder

　Melplate AU-7621 is a substitutional gold plating solution for UBM.

• ・Cyanide-free (sulfurous acid type)
• ・Deposition speed: 0.05 μm/20min
• ・Good bath stability and easy bath control
• ・Uniform Au plating film formation and good solderability
• ・Localized corrosion of Ni plating film is suppressed compared to conventional baths.

　Melplate Pal-6500 is an electroless palladium plating solution for UBM.

• ・Reduction type electroless pure palladium plating solution
• ・Excellent bath stability and selective deposition
• ・Excellent barrier to diffusion of the underlying nickel coating to the surface
• ・Good bonding properties

① Barrier property
　The electroless nickel plating Melplate NI-869 of the Melplate UBM process exhibits higher barrier properties than other baths, and the Ni/Pd/Au composition further suppresses film loss.　

② Bonding
　After reflow, Ni plating diffuses on the Au surface in the Ni/Au configuration, and wire bonding performance may deteriorate. On the other hand, in Ni/Pd/Au configuration, Ni diffusion to the surface is suppressed and stable wire bondability is achieved.　

　The Melplate UBM Process is a process for forming electroless nickel-gold and electroless nickel-palladium-gold plating films on Al electrodes. The pretreatment process of Melplate UBM process has the following features.