IC Chip Overhang and BGA Dam for Underfill Flow Control
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Solution Overview
Problem
In package-on-package (PoP) IC chip packaging, controlling underfill material flow is challenging due to tight space constraints, often leading to contamination or coverage of BGA pads, and maintaining a small integrated chip package height is difficult, especially when using flip chip plastic ball grid arrays (FC-PBGA), as conventional methods like ink dams increase cycle time and costs.
Innovation Solution
The solution involves creating an IC chip package with an overhang extending beyond its sidewall to prevent underfill material from extending over the upper surface and using a ball grid array (BGA) to surround solder elements and landing pads, effectively controlling underfill material flow and preventing overflow onto sensitive areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If underfill material is allowed to flow freely to encase C4 connectors, then reliability of electrical connections is improved, but underfill material may overflow onto BGA pads and prevent joining of packages
Solution Approach 1:
The underfill application area is segmented into two distinct zones: a first area where underfill material flows to encase C4 connectors, and a second area blocked by BGA solder elements that prevents underfill from reaching BGA pads. This spatial segmentation allows underfill to perform its bonding function while being contained away from sensitive BGA areas.
Solution Approach 2:
BGA solder elements serve as an intermediary barrier between the underfill material flow path and the BGA pads. The solder elements physically block the underfill material, preventing it from contaminating the pads while still allowing the underfill to flow around and encase the C4 connectors in the first area.
2Object-affected harmful factors
If ink dam is used to stop underfill material flow, then underfill overflow onto BGA pads is prevented, but manufacturing cycle time and costs increase
Solution Approach 1:
The BGA solder elements automatically serve as the underfill barrier during the underfill application process. The structure of the BGA package itself provides the flow-stopping function, eliminating the need for separate ink dam structures and the additional manufacturing steps required to apply and cure them.
Solution Approach 2:
The BGA solder elements perform multiple functions: they provide electrical connections between packages and simultaneously act as a barrier to underfill material flow. This multi-functionality eliminates the need for dedicated underfill barrier structures, reducing manufacturing complexity and cycle time.
3Reliability
If underfill material is applied to thin chip packages, then C4 connectors are properly encased, but underfill material bleed on top surface becomes difficult to control
Solution Approach 1:
The BGA package structure creates different local zones with different properties: the first area allows underfill flow to encase C4 connectors, while the second area with BGA solder elements creates a localized barrier that contains underfill material. This local differentiation of flow characteristics enables proper encasement while controlling surface bleed.
Data Source
AI summary
An IC chip package, in one embodiment, may include an IC chip including an upper surface including an overhang extending beyond a sidewall of the IC chip, and underfill material about the sidewall and under the overhang. The overhang prevents underfill material from extending over an upper surface of the IC chip. In another embodiment, a ball grid array (BGA) is first mounted to landing pads on a lower of two joined IC chip packages. Since the BGA is formed on the lower IC chip package first, the BGA acts as a dam for the underfill material thereon. The underfill material extends about the respective IC chip and surrounds a bottom portion of a plurality of solder elements of the BGA and at least a portion of respective landing pads thereof.