Near-Zero Standoff Component Underfilling with Thermal Epoxy
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Solution Overview
Problem
Solder joints on electrical components mounted to printed circuit boards (PCBs) often fracture due to mechanical stress caused by differences in thermal expansion coefficients between the components and the PCB substrate, especially in applications with low standoff height and high thermal and mechanical stresses, leading to impaired circuit performance.
Innovation Solution
The method involves using a thermosetting epoxy material with controlled coefficient of thermal expansion, which is heated to facilitate capillary action and completely underfills electrical components with a standoff height less than 0.15 millimeters by applying it around the perimeter of the components and curing it to enhance solder joint reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If epoxy material is used to underfill electrical components with standoff height less than 0.15 millimeters, then solder joint reliability is improved, but the epoxy material cannot completely underfill the component due to insufficient gap size
Solution Approach 1:
The patent changes the temperature parameter of the epoxy material from ambient to elevated (e.g., 80-150°C), which fundamentally alters the material's viscosity and flow characteristics. This parameter change enables the epoxy to penetrate and completely underfill components with standoff heights less than 0.15mm, resolving the contradiction between achieving complete underfill and maintaining reliability in narrow gaps.
Solution Approach 2:
The patent applies preliminary heating to the epoxy material before application, and often pre-heats the PCB and component assembly as well. This preliminary thermal preparation ensures the epoxy achieves optimal flow properties before being applied to the joint, enabling complete underfill in tight spaces and preventing subsequent reliability issues.
2Area of stationary object
If standoff height is reduced to achieve near-zero mounting, then circuit board space is improved, but solder joint fatigue resistance deteriorates due to increased mechanical stress
Solution Approach 1:
The patent applies epoxy underfill material as a protective cushioning layer between the electrical component and PCB substrate before thermal cycling occurs. This epoxy layer absorbs and distributes the mechanical stress generated by CTE differences during thermal excursions, protecting the solder joints from fatigue even when standoff height is minimized to less than 0.15mm.
Solution Approach 2:
The patent creates a composite structure by bonding epoxy material to both the PCB substrate and the electrical component, forming a tri-material system (PCB-epoxy-component). This composite construction provides mechanical reinforcement and stress distribution, enabling near-zero standoff mounting while maintaining solder joint fatigue resistance through the epoxy's compliance and adhesive properties.
3Reliability
If CTE-matched epoxy material is used to reduce thermal stress, then solder joint durability is improved, but the complexity of material selection and application increases
Solution Approach 1:
The patent specifies epoxy materials with particular parameter ranges (CTE between 0-10 ppm/°C, viscosity at specific temperatures, glass transition temperature) that can be systematically selected from commercial catalogs. By defining clear parameter specifications, the patent simplifies the material selection process while ensuring thermal stress compatibility and long-term durability of solder joints.
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 approach effectively reduces mechanical stress on solder joints by ensuring complete encapsulation and anchoring of electrical components, thereby enhancing the reliability and performance of the circuit by preventing fractures and maintaining functionality over time.
Implementation Method 1
heating the epoxy material to facilitate capillary action so the epoxy fills the smaller standoff height
Implementation Method 2
curing the epoxy material applied to the surface of the circuit board
Data Source
AI summary
The present invention relates to a method and apparatus for mounting electrical components to electric circuit boards. Specifically, the present invention relates to a method for mounting electrical components having near-zero standoff height to electrical printed circuit boards.