Polyurethane Flood Coat for Electronic Circuit Assemblies
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Solution Overview
Problem
Conventional potting materials for electronic circuit assemblies are either too thick and costly or lack sufficient mechanical integrity and vibration dampening, making them unsuitable for applications requiring reduced weight and cost while providing environmental protection and mechanical support in harsh environments.
Innovation Solution
A polyurethane flood coat composition formed by reacting a polyisocyanate prepolymer with a polyol, a rheology agent, and a catalyst, which achieves a thixotropic index of 1 to 5, a gel time of 5 to 15 minutes, and a Shore hardness of 15A to 60A, allowing for a thinner, more flexible coating that encapsulates electronic components effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional potting materials are used to provide mechanical support and environmental protection, then reliability is improved, but weight and cost increase significantly
Solution Approach 1:
The patent changes the physical and chemical parameters of the resin system by using a two-component polyurethane formulation with specific NCO:OH ratios (0.95:1.05), controlled gel times (5-15 minutes), and specific viscosity ranges (500-5000 cP). These parameter changes enable the resin to provide adequate mechanical support while flowing in thinner sections (0.05-0.5 inches) compared to conventional potting materials, reducing weight by up to 50%.
Solution Approach 2:
The invention uses a composite resin system combining polyol, polyisocyanate, catalyst, and optional fillers in specific proportions. This composite formulation integrates the benefits of flexibility (from polyol), crosslinking density (from polyisocyanate), and controlled curing (from catalyst) to achieve both mechanical support and reduced weight in a single material system.
2Reliability
If conventional potting materials are used to provide mechanical support and environmental protection, then reliability is improved, but cost increases significantly
Solution Approach 1:
The patent modifies the rheological parameters of the resin to achieve optimal flow and fill characteristics. By controlling viscosity (500-5000 cP) and thixotropic index (1.05-1.30), the resin can be applied in thinner sections (0.05-0.5 inches) while still providing adequate mechanical support, reducing material quantity and cost by up to 50% compared to traditional potting materials.
Solution Approach 2:
The invention applies resin in thinner sections (0.05-0.5 inches) than conventional potting materials, using just enough material to provide the required mechanical support and environmental protection. This partial action approach avoids the excessive material usage of traditional potting while maintaining reliability through optimized resin formulation and curing parameters.
3Weight of moving object
If thin conformal coatings are used to reduce weight and material cost, then weight and cost are reduced, but mechanical integrity and vibration dampening are insufficient
Solution Approach 1:
The patent employs a composite two-component polyurethane system that combines flexible polyol with crosslinking polyisocyanate. This composite structure provides both the thin-section capability (0.05-0.5 inches) for weight reduction and the mechanical integrity through crosslinked network formation, achieving vibration dampening and strength that thin conformal coatings cannot provide alone.
Solution Approach 2:
The invention creates local variations in resin properties by controlling the distribution of crosslinked and uncrosslinked regions during curing. The gel time control (5-15 minutes) allows the resin to maintain flowability during application then develop localized crosslinked structures that provide mechanical strength and vibration dampening where needed, while maintaining overall thin section thickness.
4Productivity
If fast-curing resins are used to reduce processing time, then productivity is improved, but re-entry capability and ease of repair are reduced
Solution Approach 1:
The patent implements a two-stage curing process where the resin first undergoes rapid initial curing (gel time 5-15 minutes) to establish basic structural integrity, then completes slower secondary curing to achieve full mechanical properties. This periodic action allows re-entry for repairs during the intermediate stage when the resin is partially cured but still workable, balancing productivity with repairability.
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 solution provides mechanical support and environmental protection to electronic components exposed to temperature extremes and vibration, reducing the overall resin weight and cost by up to 50% compared to conventional potting methods while maintaining performance properties.
Implementation Method 1
formed by reacting a polyisocyanate prepolymer A, with a polyol B
Implementation Method 2
which further contains a rheology agent/modifier C, and a catalyst D
Implementation Method 3
when a ratio of part A is mixed with a ratio of part B the mixture provides a thixotropic index from 1 to 5
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
Formulated resin systems containing polymeric flood coat compositions are provided herein and characterized by having an initial mix thixotropic index from 1 to 5, and a gel time from 5 to 15 minutes such that when cured the compositions provide a Shore hardness from 15A to 90A, a thickness on horizontal surfaces from 20 mils to 75 mils, and a thickness on vertical surfaces from 4 mils to 20 mils. Electronic circuit assemblies flood coated with such formulated resin systems, and methods for protecting and supporting said assemblies, are also provided.