Connector Formation for Solder Joint Reliability
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Solution Overview
Problem
Existing electronic device connectors with flat surfaces at the connector-connector pad interface are prone to asymmetric solder joints, leading to stress concentration and crack formation during thermal cycling, resulting in joint failure due to mismatched coefficients of thermal expansion between the bonding material and the connector-pad.
Innovation Solution
The design incorporates a connector with formations such as bends, steps, or channels that attract electrically conductive bonding material by capillary action, increasing the volume of the bonding joint while maintaining the same footprint, promoting concave surfaces at the solder-atmosphere interface and reducing stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat surface is used at the connector-connector pad interface, then the manufacturing process is simple, but the solder joint becomes asymmetric leading to stress concentration and crack formation during thermal cycling
Solution Approach 1:
The connector end is designed with an asymmetric formation (such as a bend, step, or channel) that creates a non-uniform gap between the connector and connector pad. This asymmetric geometry is intentional and designed to promote symmetric solder distribution by guiding capillary flow patterns, thereby eliminating the stress concentration issues caused by asymmetric solder joints while maintaining manufacturing feasibility.
Solution Approach 2:
The formation on the connector end introduces curved or non-linear geometric features (such as bent sections or rounded channels) that guide the solder material flow. These curved features promote uniform solder distribution by creating favorable capillary action pathways, transforming the flat surface limitation into a beneficial curved geometry that enhances joint symmetry and reliability.
2Strength
If the volume of bonding material is increased to mitigate solder crack, then the strength of the bonding joint is improved, but the footprint of the joint increases
Solution Approach 1:
Instead of increasing solder volume by expanding the joint footprint in the planar direction, the formation creates vertical dimension variations (such as bends, steps, or channels) that confine and direct solder material into a compact three-dimensional configuration. This allows increased bonding material volume to be achieved within the same footprint by utilizing the vertical dimension and creating deeper, more volumetric solder joints.
Solution Approach 2:
The formation creates a nested or layered solder distribution pattern where solder material is arranged in concentric or hierarchical configurations within the joint region. This nesting allows maximum utilization of the available footprint space, packing more bonding material into the joint volume through efficient spatial arrangement rather than simple expansion.
3Reliability
If a concave surface is formed at the solder-atmosphere interface, then stress concentration is reduced and crack formation is minimized, but the manufacturing complexity increases
Solution Approach 1:
The formation introduces localized geometric modifications (such as a single bend, step, or channel) at specific critical regions of the connector end, rather than changing the entire connector geometry. This localized approach creates the necessary concave surface configuration for stress reduction while minimizing overall device complexity and maintaining simplicity in non-critical 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
This configuration enhances the strength of the bonding joint, reduces plastic and elastic deformation under thermo-mechanical stresses, and increases the number of thermal cycling cycles the joint can withstand, achieving improved reliability by potentially passing 2500 cycles compared to 2000 cycles with traditional designs.
Implementation Method 1
an end portion of at least one of the first end and second end comprises a formation, the formation in combination with the complementary surface of one, or both, of the respective lead or the die defining therebetween a first region and at least a second region configured to attract by capillary action an electrically conductive bonding material to consolidate therein
Data Source
AI summary
An electronic device including a die and at least one lead. The electronic device further includes a corresponding at least one connector, each connector for connecting the die to a corresponding lead or leads, and each connector having a first end disposed in bondable proximity to a complementary surface of the corresponding lead and a second end disposed in bondable proximity to a complementary surface of the die. An end portion of at least one of the first end and second end has a formation, the formation in combination with the complementary surface of one, or both, of the respective lead or the die defining therebetween a first region and at least a second region configured to attract by capillary action an electrically conductive bonding material to consolidate therein.