Vented Die Attach Pad Design for Solder Void Reduction
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Solution Overview
Problem
The existing die attach process using solder often results in the formation of voids due to trapped gases, which reduces the mechanical strength of the bond between the semiconductor die and the substrate, and can lead to delamination and failure under thermal stress, especially during PCB assembly and reflow processes.
Innovation Solution
A vented die attach pad design with a patterned solder mask that includes multiple small solder segments and vent channels, allowing gases to escape and providing a safe expansion space for solder during reflow, thereby minimizing void formation and reducing the risk of solder spread and delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous solder pad is used for die attachment, then good thermal contact and mechanical strength are achieved, but large voids form in the solder due to trapped gases during reflow
Solution Approach 1:
The solder pad is segmented into multiple discrete solder segments rather than using a continuous pad. Each segment is separated by spacing that allows gas to escape during reflow, preventing large void formations while maintaining adequate thermal and mechanical contact between the die and substrate
Solution Approach 2:
The harmful trapped gas is extracted from the solder joint by providing escape paths through the spacing between solder segments. This allows gas to be removed from the system during the reflow process, eliminating the root cause of void formation
2Manufacturing precision
If solder mask completely covers the die attach area, then solder is contained within the die attach area, but gases cannot escape and voids form
Solution Approach 1:
The solder mask coverage is segmented with openings between individual solder segments. This segmentation allows the solder mask to control solder placement within each segment area while simultaneously providing gas escape paths through the openings, resolving the contradiction between containment and venting
Solution Approach 2:
The solder mask has different properties in different locations: it covers the solder segments to contain solder and provide mechanical support, but has openings in the spacing areas to allow gas escape. This local variation in mask coverage optimizes both solder control and gas venting
3Reliability
If solder is allowed to flow freely during reflow, then wetting and bonding are improved, but solder spreads beyond the die attach area causing shorts
Solution Approach 1:
The solder pad is divided into discrete segments that are spaced apart. During reflow, solder can flow and wet within each segment area to ensure good bonding, but the spacing between segments acts as a physical barrier that prevents solder from spreading beyond the die attach area, thus avoiding shorts
4Strength
If the die attach area is large to support the die, then mechanical strength is improved, but the distance for gas to escape increases leading to larger voids
Solution Approach 1:
A large die attach area is divided into multiple smaller solder segments. Each segment provides mechanical support and thermal contact, collectively maintaining overall bond strength. The spacing between segments creates multiple short gas escape paths, preventing large void formations even in large attach areas
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 vented die attach pad design significantly reduces void size and the risk of solder spread, enhancing the mechanical strength of the bond and improving the reliability of semiconductor packages by allowing gases to escape and providing balanced support to the die, leading to reduced failures and improved production yield.
Implementation Method 1
A layer of solder is formed on the substrate in a die attach area... At least one vent channel is formed through the solder mask and through the substrate... The maximum distance from any point in the solder layer to the nearest free surface of the solder at a vent channel or at the perimeter of the die is less than the distance from the center of the die to the nearest edge of the die
Implementation Method 2
heating the substrate, die, and solder to a temperature sufficient to reflow the solder
Implementation Method 3
cooling the substrate, die, and solder to a temperature sufficient to solidify the solder
Data Source
AI summary
A semiconductor device is disclosed that has a die and a substrate having a die attachment area with a perimeter. A layer of solder connects the substrate and the die, the solder layer having at least one vent channel connected to the perimeter of the die attachment area, wherein the maximum distance from any point in the solder layer to the nearest free surface of the solder at a vent channel or at the perimeter of the die is less than the distance from the center of the die to the nearest edge of the die.