Halogen-Free Adhesive Resin for Flexible PCBs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Halogen-free adhesive resin compositions for flexible printed wiring boards face challenges in maintaining adhesiveness, solder heat resistance, and flame retardancy while minimizing adhesive flow during hot pressing, which is exacerbated by the decreasing terminal diameter requirements in high-density mounting applications.
Innovation Solution
An adhesive resin composition comprising a phosphorus-containing epoxy resin, a phosphorus-containing polyester resin with a weight-average molecular weight between 20,000 and 50,000, another thermoplastic resin, preferably polyamide with reactive groups, and a benzoxazine compound, formulated to prevent adhesive overflow during hot pressing while ensuring good flow characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large amount of phosphorus flame retardant is mixed to satisfy high flame retardancy (VTM-0 or V-0 class), then flame retardancy is improved, but adhesiveness decreases
Solution Approach 1:
The patent changes the molecular weight parameter of the phosphorus-containing polyester resin from the conventional range (2,000-20,000) to a higher range (20,000-50,000). This parameter change allows the resin to provide sufficient flame retardancy while maintaining better adhesiveness and flow characteristics, resolving the contradiction between flame retardancy and adhesiveness.
Solution Approach 2:
The patent uses a composite resin system combining phosphorus-containing epoxy resin, phosphorus-containing polyester resin (with specific molecular weight), and other thermoplastic resins. This composite approach allows the different components to work synergistically, providing both flame retardancy and good adhesiveness without requiring excessive phosphorus flame retardant content.
2Strength
If the adhesive is softened and fluidized during hot pressing to improve bonding, then adhesiveness is improved, but adhesive exudes into holes impairing electrical connection
Solution Approach 1:
The patent changes the molecular weight parameter of the phosphorus-containing polyester resin to 20,000-50,000, which provides optimal balance between softening behavior during hot pressing and resistance to excessive flow. This parameter change ensures the adhesive remains sufficiently fluid for bonding while preventing harmful exusion into terminal holes.
Solution Approach 2:
The patent achieves different flow characteristics in different contexts: the adhesive exhibits sufficient fluidity at the bonding interface for good adhesion, while maintaining resistance to flow in the vertical direction to prevent exusion into holes. This local differentiation of flow behavior resolves the contradiction between adhesiveness and adhesive exusion prevention.
3Productivity
If terminal diameter is reduced for high-density mounting, then mounting density is improved, but the influence of adhesive exusion on electrical connection increases
Solution Approach 1:
The patent changes the molecular weight parameter of the phosphorus-containing polyester resin to optimize its flow characteristics, ensuring that even with reduced terminal diameters for high-density mounting, the adhesive does not exude into the smaller holes and impair electrical connections.
Solution Approach 2:
The patent applies preliminary anti-action by formulating the adhesive composition to inherently resist exusion into terminal holes before the hot pressing process occurs. The specific molecular weight range of the phosphorus-containing polyester resin pre-configures the adhesive to maintain appropriate viscosity and flow resistance, preventing the harmful effect of adhesive exusion that would be particularly problematic in high-density mounting with small terminals.
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 composition achieves balanced adhesiveness, solder heat resistance, and flame retardancy without impairing flow characteristics, making it suitable for high-density mounting applications with reduced adhesive overflow.
Implementation Method 1
a phosphorus-containing polyester resin having a weight-average molecular weight of more than 20,000 and 150,000 or less
Implementation Method 2
an adhesive resin composition, and laminates and flexible printed wiring boards using same
Data Source
AI summary
Provided are an adhesive resin composition that is halogen-free, has good adhesiveness, solder heat resistance, and flame retardancy, and has good flow characteristics, and a laminate and a flexible printed wiring board using the same. The adhesive resin composition contains a phosphorus-containing epoxy resin and/or a phosphorus-containing phenoxy resin, a phosphorus-containing polyester resin having a weight-average molecular weight of more than 20,000 and 150,000 or less, another thermoplastic resin, and a curing agent. The adhesive resin composition preferably further contains a benzoxazine compound. Preferably, substantially no inorganic filler is mixed in the adhesive resin composition.