Flip Chip Post Connect Geometry for Void-Free Solder Joints
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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 these post connects to reduce voids and enhance reliability.
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 geometry allows solder to flow outward rather than inward, eliminating the root cause of void formation and improving solder joint reliability
Solution Approach 2:
The patent changes the geometric parameter of the post connect from concave to convex. This parameter change fundamentally alters how solder interacts with the post connect during reflow, preventing the formation of voids by changing the flow dynamics and pressure distribution of the molten solder
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. The convex geometry prevents solder from being drawn inward during reflow, eliminating void formation even when connections are closely spaced, thus allowing increased productivity without sacrificing reliability
3Ease of manufacture
If conventional post connects with concave distal ends are used, then manufacturing process is simpler, but solder voids form reducing electrical performance
Solution Approach 1:
The patent inverts the post connect geometry to convex, which actually simplifies the manufacturing process by eliminating the need for complex secondary shaping operations. The convex shape is naturally formed during standard plating processes, and it inherently prevents void formation, thereby improving both ease of manufacture and solder joint quality simultaneously
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
The solution results in improved electrical performance and reliability by minimizing solder voids and maintaining a consistent contact area, reducing the number of process steps and costs.
Implementation Method 1
depositing a photoresist over the bond pads; 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
subsequently, depositing a polyimide (PI) layer over the post connects and the bond pads
Implementation Method 4
subsequently, depositing a polyimide (PI) layer over the post connects and the bond pads
Implementation Method 5
patterning the PI layer and curing the PI layer
Implementation Method 6
patterning the PI layer and curing the PI layer
Implementation Method 7
forming solder bumps on the distal ends of the post connects
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.