Monofunctional Monomers for Low-Stress Die Attach Adhesives
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Solution Overview
Problem
Current thermosetting adhesives for electronic packaging face challenges in achieving high glass transition temperatures (Tg) without increasing crosslink density, which leads to higher cure stress and modulus, and existing monofunctional monomers often result in significant weight loss during curing, causing voiding and environmental concerns.
Innovation Solution
Development of low-viscosity, mono-ethylenically unsaturated monomers that, when used alone or in combination, provide high Tg values without increasing crosslink density, thus reducing stress and modulus, and are designed to minimize weight loss during curing, incorporating specific structures and combinations with thermosetting resins and curing initiators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polyfunctional monomers are used to increase glass transition temperature, then Tg is improved, but cure stress and modulus are significantly increased
Solution Approach 1:
The patent changes the functional parameter from polyfunctional to monofunctional monomers, fundamentally altering the crosslinking behavior. This parameter change allows achieving high Tg through molecular structure design rather than crosslink density, thereby resolving the contradiction between Tg improvement and cure stress reduction
2Temperature
If polyfunctional monomers are used to increase glass transition temperature, then Tg is improved, but modulus is significantly increased
Solution Approach 1:
The patent changes the functional parameter from polyfunctional to monofunctional monomers, fundamentally altering the crosslinking behavior. This parameter change allows achieving high Tg through molecular structure design rather than crosslink density, thereby resolving the contradiction between Tg improvement and modulus reduction
3Temperature
If certain monofunctional monomers are used to achieve high glass transition temperature, then Tg is improved, but weight loss during curing is significantly increased
Solution Approach 1:
The patent changes the molecular weight parameter of monofunctional monomers, selecting low molecular weight compounds that undergo minimal volatilization during curing. This parameter change enables achieving high Tg while minimizing weight loss, resolving the contradiction between Tg improvement and weight loss reduction
4Ease of operation
If low molecular weight monofunctional monomers are used, then viscosity is reduced and ease of application is improved, but weight loss during curing is increased
Solution Approach 1:
The patent optimizes the molecular weight parameter to a specific range that balances viscosity and weight loss characteristics. This parameter optimization achieves low viscosity for easy application while selecting monomers with sufficient thermal stability to minimize curing weight loss
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 use of these monomers results in adhesive compositions with high Tg values, low stress, and low weight loss, suitable for die attach applications, offering superior interfacial stress reduction and maintaining low thermal expansion coefficients, while being environmentally friendly.
Implementation Method 1
Monofunctional, ethylenically unsaturated monomers are useful in adhesive formulations based on free radical cure because they can participate in chain extension polymerization without increasing the crosslink density of a thermoset composition
Data Source
AI summary
The invention is based on the discovery that adhesive compositions containing certain low-viscosity, mono-ethylenically unsaturated monomers have surprisingly good cure parameters, resulting in very little weight loss upon cure. Many of these monofunctional monomers used alone or in combination with other monofunctional monomers described herein have high glass transition temperatures when cured. Moreover, since these monomers are monofunctional the crosslink density of the adhesive composition does not increase (relative to multi-functional monomers), which in turns results in lower stress, lower modulus adhesive compositions. As such, these monomers are useful in a variety of thermoset adhesive compositions, such as for example, die attach adhesive compositions.