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Method for improved solder joint reliability of pads with microvias

IP.com Disclosure Number: IPCOM000132644D
Publication Date: 2005-Dec-28
Document File: 4 page(s) / 961K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for improved solder joint reliability of pads with microvias. Benefits include improved functionality, improved performance, improved reliability, and improved ease of manufacturing

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Method for improved solder joint reliability of pads with microvias

Disclosed is a method for improved solder joint reliability of pads with microvias. Benefits include improved functionality, improved performance, improved reliability, and improved ease of manufacturing.

Background

              Microvias in pads are conventional features on circuit boards for high input/output (I/O) density applications. They enable finer ball-pitch BGA packages and save space on the board. However, process voiding can result from this design.

              Process voiding at the microvia creates a solder joint reliability (SJR) issue on the second-level interconnects (SLI). Voids concentrate stress within the solder joint and can cause cracks to initiate from within the microvia regions (see Figure 1).

              The thermo-mechanical fatigue impacts high stress locations, such as package corners. The issue is severe in lead-free solder systems that have more stiffness and larger voids.

              Conventionally, no cracking is reported on solder joints without voids in the microvias. As a result, microvia filling and capping are being implemented to eliminate the voiding. The additional processing increases the fabrication cost (see Figure 2).

              Process control, especially in screen printing and reflow, has been explored to reduce void size. However, this approach reduces the process margin by requiring tight process control. X-ray inspection systems have been the last resort in screening out materials with voids exceeding the threshold limit. However, the equipment adds high capital equipment costs and lengthens the manufacturing through-put time.

              The wireless and cell phone industries require high input/output (I/O) density due to the small form factors. As a result, microvia designs are compulsory.

General description

              The disclosed method is a corner ball-grid array (BGA) package pad design to improve the fatigue life of pads with microvias. Thick trace pads contain microvias that are not oriented to the corners of the BGA package.

              The disclosed method can be applied to any BGA ball pitch without resulting in additional bridging.

Advantages

              The disclosed method provides advantages, including:
•             Improved functionalit...