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Refractory Metal or Insulator Moat to Curb Progression of Undercut in C4 Underbump Metallurgy (UBM) During Isotropic Wet Etch

IP.com Disclosure Number: IPCOM000248480D
Publication Date: 2016-Dec-06
Document File: 3 page(s) / 109K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method applied to underbump metallurgy that significantly reduces the extent of undercut during the wet etch process by creating a moat or ring over the final passivation with a material that can act as an etch stop.

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Title

Refractory Metal or Insulator Moat to Curb Progression of Undercut in C4 Underbump Metallurgy (UBM) During Isotropic Wet Etch

Abstract

Disclosed is a method applied to underbump metallurgy that significantly reduces the extent of undercut during the wet etch process by creating a moat or ring over the final passivation with a material that can act as an etch stop.

Problem

The underbump metallurgy (UBM) used as a barrier for an existing Copper/Tin/Silver (Cu/Sn/Ag) solder bump is Titanium Tungsten (TiW). Wet etch is used to remove the sputtered TiW and Cu seed between the solder bumps, post solder plating, and resist strip. The wet etch process is isotropic and leads to about 1-2um of horizontal undercut in the Cu seed and 1-2um horizontal undercut in the TiW UBM sputtered layers. This reduction in the area of the UBM structure under the solder bumps leads to localized joule heating and subsequent reliability electromigration fails of the solder bumps. The undercut could also act as a stress concentrator and initiation point for cracks to propagate into the chip during the chip-join reflow process, leading to chip packaging interaction (CPI) fails. The issue is further exacerbated with the reduction in bump diameters and pitch in newer two-, two-and-a-half-, and three-dimensional (2D, 2.5D and 3D) technologies.

Figure 1: Illustration of the problem

A structure is needed that significantly reduces the extent of undercut during the wet etch process by creating a moat or ring over the final passivation with a material that can act as an etch stop.

Solution/Novel Contribution

The novel solution is to creat...