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Method for a simple low-cost approach to improve the ball coplanarity of organic packages

IP.com Disclosure Number: IPCOM000010734D
Publication Date: 2003-Jan-15
Document File: 8 page(s) / 399K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a simple low-cost approach to improve the ball coplanarity of organic packages. Benefits include improved functionality, improved reliability, and improved ease of manufacturing.

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Method for a simple low-cost approach to improve the ball coplanarity of organic packages

Disclosed is a method for a simple low-cost approach to improve the ball coplanarity of organic packages. Benefits include improved functionality, improved reliability, and improved ease of manufacturing.

Background

        � � � � � Conventionally, the ball coplanarity of large packages is high, causing assembly issues during subsequent surface mount applications. No proven solution exists for this problem. Attaching a lid to the package is an option. A number of options are being evaluated, including attaching a window-frame stiffener to the die side of the substrate using an adhesive (see Figure 1).

        � � � � � For a metallic window-frame stiffener to be truly effective, it must be rigidly coupled to the substrate. The elastic modulus of the adhesive used to attach the stiffener to the substrate should be high. If a stiff adhesive is used, CTE mismatch between the substrate and the stiffener material can cause solder mask and build-up cracks near the stiffener. By rigidly coupling the metallic stiffener to the substrate, the effective flexural stiffness of the substrate increases. This approach increases the force on the BGAs during handling and shock/vibration events, increasing the likelihood of brittle solder joints and similar failures.

General description

� � � � � The disclosed method is simple low-cost approach to improve the ball coplanarity of organic packages. The method’s goal is to reduce the ball coplanarity of organic packages and bring them within the 8-mil specification.

� � � � � The key elements of the method include:

•        � � � � Die-side window frame-like structure made of the standard build-up material to tailor the CTEs of the layers above and below the core (B and F layers)

•        � � � � The resulting CTE mismatch-induced warpage within the substrate warps the substrate in a direction opposite to that caused due to the die-substrate CTE mismatch, reducing the ball coplanarity

� � � � � The disclosed method is much less expensive than using a lid to improve the ball coplanarity. Because the added standard build-up material window frame layer is incorporated into the substrate manufacturing process, the part arrives in-house with the stiffener build-in, simplifying the assembly process (see Figure 2).

Advantages

        � � � � � The disclosed method provides advantages, including:

•        � � � � Improved functionality due to meeting the 8-mil coplanarity standard

•� � � � Improved reliability due to defect reduction because of reduced ball coplanarity

•        � � � � Improved ease of manufacturing due to simplifying the assembly process by including the stiffener as part of the substrate

•        � � � � Improved cost effectiveness due to simplifying the assembly process by including the stiffener as part of the substrate

Detailed description

� � � � � The disclosed method is a simple low-cost approach to improve the ball coplanarity of organic packages.

        � �...