Chamfered Solder Injection Head for Uniform Via Filling
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Solution Overview
Problem
In injection molded solder (IMS) technology, fine pitch bumping faces challenges such as solder bump height variation and missing solder in vias due to surface roughness and residual gas pressure, leading to electrical shorts and mechanical failures.
Innovation Solution
The IMS head is modified with chamfered edges to improve sealing and vacuum performance, and a second injection slit is added to compensate for missing solder, along with differential surface roughness for better conductance and sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If injection pressure is increased to prevent missing solder in vias, then solder filling is improved, but head rubber deteriorates earlier due to increased frictional force
Solution Approach 1:
The patent applies preliminary evacuation of gas from vias before solder injection. By removing residual gas in advance, the injection process requires lower pressure to achieve complete solder filling, thereby preventing premature head rubber deterioration while ensuring reliable solder placement in fine pitch vias.
2Reliability
If load on head is increased to improve sealing and reduce residual gas pressure, then vacuum sealing is improved, but frictional force between head and wafer increases causing early head rubber deterioration
Solution Approach 1:
The patent introduces differential surface roughness on the head contact surface, with smoother regions positioned at sealing locations and rougher regions at scraping locations. This local differentiation allows effective sealing with lower overall load, reducing frictional force and preventing premature head rubber deterioration while maintaining vacuum integrity.
3Manufacturing precision
If surface roughness of IMS head is high, then solder scraping and height control is improved, but solder bump height variation increases
Solution Approach 1:
The patent implements differential surface roughness with distinct smooth and rough regions on the head contact surface. Smooth regions provide consistent scraping action for uniform solder bump heights, while rough regions enhance solder adhesion. This local differentiation simultaneously improves height precision and electrical connection reliability.
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 chamfered edges enhance vertical stress for leveling molten solder and improve bump height consistency, while the additional slit ensures complete filling of vias, reducing solder height variation and mechanical failures.
Implementation Method 1
an evacuating device connected to the injection head for evacuating gas from the via holes
Implementation Method 2
the surface tension of molten solder and the residual gas pressure in vias
Implementation Method 3
The injection head has a chamfer part on an edge of a contact surface contacting the top surface of the wafer
Implementation Method 4
the surface roughness of the IMS head can be as much as several dozen microns at room temperature. Since the solder bump height is determined by the scraping of molten solder by the IMS head surface
Data Source
AI summary
An apparatus for injecting solder material in via holes located in a top surface of a wafer is provided. The apparatus includes an injection head having a contact surface for contacting the top surface of the wafer, and at least one aperture for injecting the solder material though the injection head into the via holes. The apparatus further includes an evacuating device connected to the injection head for evacuating gas from the via holes. The injection head has a chamfer part on an edge of a contact surface contacting the top surface of the wafer.