Flip Chip Post Connect Geometry to Minimize Solder Voids
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Solution Overview
Problem
In flip chip packaging, voids in solder joints form due to solder shrinkage and the concave shape of post connects, leading to reduced electrical performance and reliability issues.
Innovation Solution
A method involving forming post connects with convex or flat distal ends, using a polyimide layer to cover the sides and bond pads, and depositing solder bumps on the distal ends to reduce void formation during thermal reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder reflow process is used to mount semiconductor die to package substrate, then mechanical attachment and electrical coupling are achieved, but voids form in solder joints due to solder shrinkage and concave shape of post connects
Solution Approach 1:
The patent inverts the conventional concave post connect shape to a convex shape. This inversion prevents solder shrinkage from creating voids during the reflow process, as the convex shape allows solder to flow outward and maintain contact with both the post connect and package substrate, eliminating the void formation problem while maintaining reliable mechanical and electrical connection
Solution Approach 2:
The patent changes the geometric parameter of the post connect from concave to convex shape. This parameter change fundamentally alters how solder behaves during reflow, preventing the formation of voids by ensuring continuous solder contact with the bonding surfaces, thereby improving both manufacturing precision and joint reliability
2Productivity
If pitch distance between conductive post connects is decreased to increase connection density, then number of connections increases, but void formation in solder joints increases
Solution Approach 1:
By inverting the post connect shape to convex, the patent enables higher connection density at reduced pitch distances without compromising solder joint quality. The convex shape ensures that even at closer spacing, solder flows properly and maintains contact with bonding surfaces, preventing void formation that would otherwise occur with high-density concave post connects
3Ease of manufacture
If conventional post connects with concave distal ends are used, then manufacturing process is simpler, but solder joints exhibit reduced electrical performance due to voids
Solution Approach 1:
The patent inverts the post connect shape to convex, which actually simplifies the manufacturing process by eliminating the need for complex concave shaping steps. The convex shape can be achieved through standard plating processes, and simultaneously improves electrical performance by preventing void formation that disrupts current flow paths
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in improved electrical performance and reliability by minimizing solder voids and maintaining contact with the package substrate, enhancing the mechanical and electrical connection between the semiconductor die and the package substrate.
Implementation Method 1
patterning the photoresist to form openings over the bond pads
Implementation Method 2
performing a plating process to form post connects in the openings
Implementation Method 3
depositing a polyimide (PI) layer over the post connects and the bond pads; patterning the PI layer and curing the PI layer
Implementation Method 4
the solder bumps at the distal end of the post connects are subjected to a thermal reflow process so that the solder melts and flows to form solder joints
Data Source
AI summary
In a described example, an apparatus includes: a semiconductor die having a device side surface; bond pads on the semiconductor die on the device side surface; post connects having a proximate end on the bond pads and extending from the bond pads to a distal end, the diameter of the post connects at the proximate end being the same as the diameter of the post connects at the distal end; polyimide material covering sides of the post connects and covering at least a portion of the bond pads; and solder bumps on the distal end of the post connects.