Flat Solder Bump with Non-Metallic Core for BGA
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Solution Overview
Problem
Solder ball structures in ball grid arrays (BGAs) face issues of electrical connection degradation due to solder cracks and stand-off height variations, leading to reliability concerns.
Innovation Solution
The implementation of a solder bump structure with a non-metallic core, such as a plastic core, surrounded by a conductive layer, which provides a stable standoff height and reduces stress, thereby preventing solder bridging and cracking, and features a flat shape with a bump height to width ratio of 0.05 to 1, enhancing contact area and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional solder ball structures are used in BGA, then manufacturing is simpler, but electrical connection reliability deteriorates due to solder cracks and stand-off height variation
Solution Approach 1:
The solder bump is divided into multiple functional layers: a non-metallic core providing structural stability and stand-off height control, a conductive layer for electrical connection, and an outer solder layer for bonding. This segmentation allows each layer to optimize its specific function, improving overall reliability while managing complexity through functional specialization.
Solution Approach 2:
The invention uses composite structure combining non-metallic core material with metallic conductive and solder layers. This composite approach leverages the advantages of different materials: the non-metallic core provides dimensional stability and crack resistance, while the metallic layers provide electrical conductivity and bonding capability, thereby improving reliability.
2Manufacturing precision
If solder ball structures are used, then device complexity is lower, but stand-off height variation increases leading to connection degradation
Solution Approach 1:
The non-metallic core is formed first with precise dimensional control before adding the conductive and solder layers. This preliminary formation of the core structure establishes the stand-off height early in the manufacturing process, ensuring consistency across all solder bumps and reducing height variation.
Solution Approach 2:
The invention changes the fundamental parameter of stand-off height control from relying on solder material properties to being determined by the non-metallic core dimensions. This parameter change enables more precise and consistent stand-off height control since the core can be manufactured with tighter tolerances than traditional solder balls.
3Reliability
If flat solder bump shape with low height-to-width ratio is used, then contact area increases improving reliability, but manufacturing precision requirements increase
Solution Approach 1:
The flat bump shape is achieved by segmenting the structure into a cylindrical non-metallic core with flat top and bottom surfaces, covered by conductive and solder layers. This segmentation makes it easier to control the overall flat shape and low height-to-width ratio, as the core geometry directly determines the bump profile.
Solution Approach 2:
The invention changes the bump shape parameter from spherical to flat with low height-to-width ratio (0.05 to 1). This parameter change increases the contact area for better electrical connection and mechanical bonding, while the segmented structure with non-metallic core facilitates achieving this shape with controlled precision.
Data Source
AI summary
A solder bump structure for a ball grid array (BGA) includes at least one under bump metal (UBM) layer and a solder bump formed over the at least one UBM layer. The solder bump has a bump width and a bump height and the ratio of the bump height over the bump width is less than 1.