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Method for a groove ring on a connection pad for better solder joint reliability

IP.com Disclosure Number: IPCOM000033862D
Publication Date: 2004-Dec-30
Document File: 5 page(s) / 89K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a groove ring on a connection pad for better solder joint reliability. Benefits include improved performance and improved reliability.

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Method for a groove ring on a connection pad for better solder joint reliability

Disclosed is a method for a groove ring on a connection pad for better solder joint reliability. Benefits include improved performance and improved reliability.

Background

              Second-level interconnections can failure during reliability stress testing. The typical reliability stresses are temperature cycles and shock and vibration. Temperature cycles are used to assess the operating life of the product. Shock and vibration are used to simulate the shipment and handling environment. The typical failure is either solder fatigue or brittle joint cracking at high-stress areas. Cracks occur between the solder ball and the component/board metal pad interface.

      Conventionally, the problem is solved by adding solder joint thermomechanical strength with the following techniques:
•             Increasing the metal pad diameter opening

•             Using larger solder balls

•             Increasing the stand-off height

•             Adding sacrificial balls in high-stress areas on the component ball fields

              No enhancement is expected to the copper pad. The pad itself is not a source for improving  solder joint reliability. As the pitch is getting tighter from 1.27-mm to 1.00-mm to 0.8-mm ball pitch, improving solder-joint strength and reliability is very challenging.

              A conventional 1-mm pitch solder ball results in a pad diameter of 460 µm (see Figure 1). The relationship between the pitch size and pad diameter can be expressed using the following equation:

Area =  = 3.142 * (230)2

                    = 166190 µm2

General description

              The disclosed method includes groove rings on the copper pad to provide more surface area for the solder joint, increasing the robustness of the solder joint.

Advantages

              The disclosed method provides advantages, including:

•             Improved performance due to increased contact area because the grooves on the copper pad

•             Improved reliability due to increasing the pad’s surface area

Detailed description

      The disclosed method includes groove rings on the copper pad (see Figure 2). The method uses the conventional process to create the flip-chip ball-grid array (FC-BGA) package, including the solder ball pad. Additional masking and photolithography are used to create the grooves for the ball pad. The surface is plated with Ni/Au plat...