Metallized Thermoplastic Interlayer for PCB Diffusion Bonding
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Solution Overview
Problem
Conventional methods for connecting metallized layers in printed circuit boards face challenges such as adapting hole diameters to layer thickness and limiting antenna effects, particularly in multilayer circuits with microwave functions, where the density of connections is restricted due to the use of pre-impregnated adhesive layers and multiple tangent holes.
Innovation Solution
The method involves using metallized thermoplastic intermediate layers with drilled holes, metallizing the holes, applying different metals to the hole openings, and pressing the layers together at the thermoplastic's melting temperature to facilitate intermetallic diffusion bonding, allowing for increased hole density and reliable connections without the risks associated with sticky pre-impregnated layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-impregnated adhesive layers are used to bond metallized layers, then the layers can be connected together, but the adhesive material creeps during circuit formation and limits connection density
Solution Approach 1:
The patent changes the physical state of the bonding material from a sticky pre-impregnated adhesive to a thermoplastic material that transitions from solid to liquid and back to solid through controlled heating and cooling cycles, eliminating creep while maintaining bonding capability
Solution Approach 2:
The thermoplastic intermediate layer undergoes phase transition between solid and liquid states during processing: it melts during pressing to allow metallized holes to pass through and bond, then solidifies upon cooling to provide structural support without creep, enabling higher connection density
2Productivity
If multiple tangent holes are drilled in intermediate layers to increase connection density, then more connections can be made, but the layers become very difficult to handle
Solution Approach 1:
The thermoplastic material's temperature-dependent properties allow the intermediate layer to be flexible and easy to handle at room temperature, but become moldable and conformable during heating/pressing operations, facilitating handling even with multiple tangent holes
3Reliability
If hole diameter is adapted to layer thickness for reliable through holes, then connection reliability improves, but antenna effects increase in microwave circuits
Solution Approach 1:
The patent uses a composite structure with thermoplastic intermediate layers and metallized holes, where the thermoplastic material provides mechanical support and the metallized portions provide electrical connection, allowing optimized hole dimensions that balance reliability and antenna effect mitigation
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 enhances the density of connections and prevents metallization creep, enabling more efficient and reliable electrical connections while minimizing antenna effects, particularly in multilayer circuits with microwave functions.
Implementation Method 1
pressing of the metallized layers and of the said superimposed interlayers, so as to bond by diffusion the areas covered with a first metal with the areas covered with a second metal which are in contact
Implementation Method 2
bond by diffusion the areas covered with a first metal with the areas covered with a second metal which are in contact
Data Source
Figure 1
Figure 2
AI summary
The method involves superimposing two layers, and metallizing two faces of each layer. An interlayer made of metallized thermoplastic material e.g. liquid crystal polymer, is arranged between the two layers. Holes are pierced within the two layers before the two layers are placed in contact with each other, and within the interlayer. The holes are metallized. A metal is applied on openings of the holes of the two layers, and another metal is applied on openings of the holes of the interlayer. The two layers and the interlayer are pressed for diffusion bonding of zones covered with the metals. An independent claim is also included for a printed circuit board comprising two superimposed metallized layers.