Browse Prior Art Database

Method for selective substrate trace shielding

IP.com Disclosure Number: IPCOM000029148D
Publication Date: 2004-Jun-16
Document File: 4 page(s) / 149K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for selective substrate trace shielding. Benefits include improved functionality, improved performance, and improved reliability.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 54% of the total text.

Method for selective substrate trace shielding

Disclosed is a method for selective substrate trace shielding. Benefits include improved functionality, improved performance, and improved reliability.

Background

              Standard copper plating techniques are used to manufacture substrates (see Figures 1 and 2). However, copper can migrate within the substrate. During operation or highly accelerated stress test (HAST) package testing, adjacent biased traces within a substrate have a tendency to act as a cathode/anode. Additionally, copper ions (dendrites) begin to grow from one trace to the adjacent, opposite biased trace. The result is called the halo effect (see Figure 3).

              To solve this problem, several approaches have been used, such as:

•             Tightly control allowable minimum space between two adjacent traces.

•             Modulate solder-mask ink material type and properties to minimize the likelihood of dendrite growth.

•             Tightly control plating, etching, and rinse processes to ensure no residue is left between adjacent traces to induce or permit dendrites to grow.

General description

      The disclosed method is selective substrate trace shielding to prevent copper migration in substrates. A thin layer of material is used on the sidewalls of copper traces and planes within a substrate to inhibit copper migration during operation (bias).

Advantages

              The disclosed method provides advantages, including:

•             Improved functionality due to placing a diffusion barrier on the sidewall of all copper traces and planes

•             Improved functionality due to enabling denser routing with the same trace width manufacturing process

•             Improved performance due improving the signal integrity and power delivery

•             Improved reliability due to preventing dendrites to grow

Detailed description

 

              The disclosed method includes the application of a thin diffusion barrier. This barrier can be one of several elements. For example, a nickel layer can be deposited. The nickel acts as a barrier to ionic movement of copper beyond the nickel. The barrier is applied only to the sidewalls of exposed areas of the copper trace and planes (see Figure 4).

      The diffusion barrier could also be organic in nature, such an organic solderability preservative (OSP) type application.

      The key element of the disclosed method is the application of the diffusion barrier selectively to the sidewalls of the traces and planes in the substrate. The key reason is signal integrity and power delivery. Coating the entire surface with Ni (or cobalt or iron) is not a good idea. It increases self-inductance and resistance considerably, which increases switching noise. Modeling indicates that any significant thickn...