Copper Pillar Solder Joint Thermal Stress Mitigation
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Solution Overview
Problem
Conventional semiconductor device contacts face challenges with thermal stresses and reliability due to heat generation, leading to potential damage and failure.
Innovation Solution
A robust pillar structure is introduced, comprising a copper pillar on a mushroom-shaped or cylindrical post with a solder brace, which alleviates thermal stress by creating a 'zig-zag' interface between the copper and solder, enhancing solder joint reliability and electromigration performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional semiconductor device contacts are used, then device structure is simple, but thermal stresses damage contacts and reliability deteriorates
Solution Approach 1:
The contact structure is divided into multiple segments: a copper pillar, a mushroom-shaped or cylindrical post, and a solder brace. This segmentation allows each component to perform its specific function - the pillar provides electrical connection, the post distributes mechanical stress, and the solder brace absorbs thermal expansion differences, thereby improving reliability while managing complexity through functional division
Solution Approach 2:
The contact structure employs composite materials with different properties - copper for electrical conductivity, solder material for thermal and mechanical compliance. This composite approach allows the structure to simultaneously achieve electrical connectivity, thermal stress management, and mechanical robustness, resolving the contradiction between reliability improvement and structural complexity
2Productivity
If heat is generated in semiconductor die, then device operation is enabled, but thermal stresses damage contacts
Solution Approach 1:
The solder brace layer is specifically designed to accommodate and convert the harmful thermal expansion stresses into beneficial mechanical compliance. The solder material's intermediate thermal expansion coefficient between copper and the substrate allows it to absorb thermal stresses while maintaining electrical connectivity, effectively converting the harmful thermal effect into a stress-relief mechanism
Solution Approach 2:
The invention changes the physical parameters of the contact structure by introducing layers with different thermal expansion coefficients and mechanical properties. The copper pillar provides low thermal expansion, the solder brace provides intermediate compliance, and the substrate provides structural support. This parameter differentiation allows the structure to operate under thermal conditions without damage
3Reliability
If current density is concentrated in contacts, then electrical connection is established, but current crowding accelerates failure
Solution Approach 1:
The mushroom-shaped post extends the current path into additional spatial dimensions, distributing current density across a larger volume. The flared geometry of the mushroom shape provides multiple current flow paths through its expanded top surface, reducing current crowding at any single point and thereby improving contact durability
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 pillar structure improves solder joint reliability by distributing thermal strain and reducing current crowding, thereby delaying failure and increasing the reliability of semiconductor device contacts.
Implementation Method 1
alleviates thermal stress by creating a 'zig-zag' interface between the copper and solder
Implementation Method 2
enhancing solder joint reliability and electromigration performance
Data Source
AI summary
Methods and systems for a robust pillar structure for a semiconductor device contacts are disclosed, and may include processing a semiconductor wafer comprising one or more metal pads, wherein the processing may comprise: forming a second metal contact on the one or more metal pads; forming a pillar on the second metal contact, and forming a solder bump on the second metal contact and the pillar, wherein the pillar extends into the solder bump. The second metal contact may comprise a stepped mushroom shaped bump, a sloped mushroom shaped bump, a cylindrical post, and/or a redistribution layer. The semiconductor wafer may comprise silicon. A solder brace layer may be formed around the second metal contact. The second metal contact may be tapered down to a smaller area at the one or more metal pads on the semiconductor wafer. A seed layer may be formed between the second metal contact and the one or more metal pads on the semiconductor wafer. The pillar may comprise copper.