Browse Prior Art Database

Method for exposed solder-ball molding of a stress compensation layer

IP.com Disclosure Number: IPCOM000100631D
Publication Date: 2005-Mar-16
Document File: 4 page(s) / 81K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for exposed solder-ball molding of a stress compensation layer (SCL). Benefits include improved functionality, improved performance, improved yield, improved process simplicity, and improved ease of manufacturing.

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 53% of the total text.

Method for exposed solder-ball molding of a stress compensation layer

Disclosed is a method for exposed solder-ball molding of a stress compensation layer (SCL). Benefits include improved functionality, improved performance, improved yield, improved process simplicity, and improved ease of manufacturing.

Background

      The reliability of solder-joints formed by stressed solder balls on ball-grid array (BGA) packages must be improved (see Figure 1). Solder-joint reliability (SJR) is expected to be a major issue as the size of packages and solder ball pitch shrinks. Additionally, the implementation of the lead-free materials required by legislation is expected to exacerbate the SJR issue.

      To improve reliability, specific design rules, such as using a component pad-to-board pad aspect ratio of 0.9-1.1, are intended to reduce the stress on solder balls. Solder balls at the component corners, which are more prone to SJR failure, can be encapsulated with underfill. However, this solution only reinforces the solder balls at the periphery of the component. Those solder balls at the center of the component are not encapsulated.

      Another conventional solution is the dispensing and printing of SCL materials on the component. Solder ball contamination is the major issue when SCL material is printed or dispensed on the package. Furthermore, the assembly rate (units per hour, UPH) of using the dispense method is low because the SCL material is dispensed line by line between the solder balls. These solutions are not suitable for high volume manufacturing (HVM).

      Alternatively, epoxy flux can be used for encapsulation. It is a type of flux material that cross-links and encapsulates the collar of the solder joint of the component. However, this solution only encapsulates the solder balls of the component and is a very costly material.

      Transfer molding is a well-established process. Flip-chip molded matrix array packages have

proven the use of highly compressible polymer film to reduce mold flash.

General description

      The disclosed method is the exposed solder ball molding of a stress compensation layer (SCL). A layer of highly compressible polymer film is inserted between the solder balls and a mold die is used to prevent molding materials from flashing on the solder balls. This technique eliminates the contamination of solder ball by SCL materials that prevent board attachment. The assembly UPH rate of the SCL process is increased because of the high through-put-time (TPT) of the molding process. 

Advantages

              The disclosed method provides advantages, including:

•             Improved functionality due to the capability to be used for any aspect ratio, solder ball size and pitch

•         ...