Metal Mask for Solder Flow Control on Circuit Boards
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Solution Overview
Problem
Conventional solder masks made of organic materials are inadequate as they introduce a step that acts as a stress concentrator and cannot withstand high temperatures, leading to undesirable solder wetting and potential joint deformation in electronic circuit board applications.
Innovation Solution
A metal mask is used to restrict solder flow from protected areas by forming a solder wettable surface and employing metals like titanium, tungsten, and chromium, which do not metallurgically bond with solder, and can withstand high temperatures, with a thickness less than 125 microns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If organic solder mask is used to protect areas from solder, then solder flow restriction is achieved, but stress concentration occurs at the step between solderable and protected surfaces
Solution Approach 1:
The patent extracts the harmful step structure by applying a conformal coating that fills and eliminates the step between solderable and protected surfaces. The coating material is applied to conformally cover the step, removing the stress concentration point while maintaining the protective function of the solder mask.
Solution Approach 2:
The patent applies different properties to different locations: the conformal coating provides stress relief at the step location, while the solder mask maintains its protective function in protected areas. This local differentiation of material properties resolves the contradiction between protection and stress concentration.
2Object-affected harmful factors
If organic solder mask is used to restrict solder flow, then area protection is achieved, but the mask cannot withstand high temperatures leading to unwanted solder wetting
Solution Approach 1:
The patent uses a composite structure combining organic solder mask material with an inorganic conformal coating material. The conformal coating provides high-temperature resistance while the organic mask provides solder flow restriction. This composite approach allows the system to withstand temperatures above 200°C while maintaining protection functionality.
3Stability of the object's composition
If thicker organic solder mask is used to improve temperature resistance, then thermal stability is improved, but the step structure becomes more pronounced increasing stress concentration
Solution Approach 1:
The patent employs a thin conformal coating that flexibly conforms to the underlying step structure rather than adding significant thickness. This thin film approach provides the necessary thermal stability and stress relief without creating a pronounced step, thus avoiding increased stress concentration.
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 metal mask effectively confines solder to intended areas, preventing unwanted wetting and deformation, while maintaining structural integrity at elevated temperatures, enabling efficient and reliable soldering processes.
Implementation Method 1
employing metals like titanium, tungsten, and chromium, which do not metallurgically bond with solder
Implementation Method 2
forming a solder wettable surface
Data Source
AI summary
A circuit board includes a solder wettable surface and a metal mask configured to restrict solder from flowing outside the solder wettable surface of the circuit board.