Surface Mount Device Contact Positioning for Stress Mitigation
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Solution Overview
Problem
Surface mount devices (SMDs) experience mechanical stress and failure due to differences in thermal expansion coefficients between the substrate, solder, and carrier, leading to separation of electrical contacts from the carrier, especially at the edges, resulting in high failure rates.
Innovation Solution
The SMDs are designed with electrical contacts located within a lateral distance less than 50% of the substrate's width from the center, and the thermal pad is physically separated into sections by a solder mask to create mechanical breaks, reducing stress and preventing defect propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electrical contacts are located at the outer edges of the substrate to maximize circuit functionality, then the device can provide more electrical connection points, but the mechanical stress on the electrical contacts increases significantly leading to separation from the carrier
Solution Approach 1:
The patent segments the substrate into distinct functional zones: an inner region containing electrical contacts positioned within 50% of the substrate width from the center, and an outer region containing the thermal pad. This spatial segmentation allows electrical contacts to be positioned in the lower-stress inner region while the thermal pad handles heat dissipation in the outer region, resolving the contradiction between electrical connectivity and mechanical reliability
Solution Approach 2:
The patent applies local quality by assigning different functional characteristics to different regions of the substrate. The inner region is optimized for electrical connections with contacts positioned to minimize mechanical stress, while the outer region is optimized for thermal management. This localized functional differentiation allows each region to perform its specific function optimally without compromising the other
2Temperature
If the thermal pad is positioned at the center to maximize heat dissipation efficiency, then thermal management is improved, but the electrical contacts must be positioned at the edges which increases mechanical stress and failure rate
Solution Approach 1:
The patent segments the substrate into distinct functional zones: an inner region containing electrical contacts positioned within 50% of the substrate width from the center, and an outer region containing the thermal pad. This spatial segmentation allows electrical contacts to be positioned in the lower-stress inner region while the thermal pad handles heat dissipation in the outer region, resolving the contradiction between electrical connectivity and mechanical reliability
Solution Approach 2:
The patent resolves the spatial conflict between thermal pad and electrical contacts by utilizing the dimensional space effectively. By positioning electrical contacts in the inner region (within 50% width from center) and the thermal pad in the outer region, the patent creates a radial distribution pattern that optimizes both thermal and electrical functions simultaneously, transforming the positioning problem from a one-dimensional conflict to a two-dimensional spatial optimization
3Reliability
If the substrate material is selected for optimal electrical conductivity, then electrical performance is improved, but the coefficient of thermal expansion mismatch with solder and carrier increases leading to higher mechanical stress
Solution Approach 1:
The patent addresses the CTE mismatch issue by changing the spatial parameter of electrical contact positioning rather than changing material properties. By positioning electrical contacts within 50% of the substrate width from the center, the patent reduces the lever arm and moment arm lengths, thereby reducing the mechanical stress and deformation caused by CTE mismatch during thermal cycling, even when using highly conductive materials
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 design significantly reduces mechanical stress on electrical contacts and thermal pads, thereby decreasing the failure rate of SMDs by preventing separation from the carrier and extending their functional lifespan.
Implementation Method 1
differences in the coefficient of thermal expansion (CTE) between the substrate 12 of the conventional SMD 10, the solder 30, and the carrier 28 generate mechanical stress
Data Source
AI summary
An SMD includes a substrate and one or more electrical contacts on a first surface of the substrate. Each one of the electrical contacts are configured to couple to a corresponding electrical contact located on a surface of a carrier, and are located within a concentric area of the first surface that is less than about 50% of a total area of the first surface. By providing the electrical contacts within the concentric area, the mechanical stress experienced by the electrical contacts can be significantly reduced when compared to conventional SMDs including electrical contacts on the outer edges thereof. Accordingly, the failure rate of the SMD due to separation of one or more of the electrical contacts from the carrier may be reduced.