Multilayer Wiring Board via Hole Alloying
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Solution Overview
Problem
Current methods for manufacturing multilayer wiring boards face challenges such as limited thickness reduction, surface roughness, and long-term reliability issues, particularly when using pre-preg materials and conductive pastes that require cap plating or result in insufficient conductivity and stability.
Innovation Solution
A method involving preheating pre-preg to reduce the storage modulus ratio, filling via holes with alloying paste containing metal powders that melt and alloy, and pressing copper layers onto the paste to achieve superior conductivity and stability without cap plating, using a pre-preg with a specific resin composition and metal powder mixture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If through hole plating and cap plating are applied to ensure conductivity and reliability, then long-term stability is improved, but board thickness increases and fine patterning becomes difficult
Solution Approach 1:
The invention extracts and eliminates the cap plating process from the conventional manufacturing flow. By using alloying paste that forms conductive pathways through direct alloying with copper layers during pressing, the patent removes the need for additional cap plating, thereby reducing board thickness while maintaining conductivity and reliability.
Solution Approach 2:
The invention changes the physical and chemical parameters of the conductive paste by using alloying paste containing low-melting-point metals. This paste undergoes phase change during pressing to form alloy bonds, replacing the need for cap plating and enabling fine patterning while ensuring long-term stability through metallurgical bonding.
2Length of stationary object
If powder contact paste is used to achieve conductivity without cap plating, then board thickness is reduced, but surface roughness increases and long-term reliability becomes insufficient
Solution Approach 1:
The invention changes the material composition and physical properties of the conductive paste by using alloying paste instead of powder contact paste. The alloying paste contains low-melting-point metals that undergo phase change during pressing to form strong alloy bonds with copper layers, ensuring both smooth surface finish and long-term reliability while maintaining reduced board thickness.
Solution Approach 2:
The invention uses composite alloying paste materials combining resin components with metal powders including low-melting-point metals. This composite material provides both the filling function and the alloying function, creating strong metallurgical bonds that ensure long-term stability while enabling fine patterning and smooth surfaces.
3Ease of manufacture
If preheating is not performed to maintain pre-preg flexibility, then ease of manufacture is improved, but conductive paste spreading occurs and resin-paste mixing prevents desired characteristics
Solution Approach 1:
The invention applies preliminary preheating treatment to the pre-preg before filling with conductive paste. This preliminary action partially cures the resin, reducing its flow characteristics and preventing paste spreading during subsequent pressing, while still allowing easy via hole formation and paste filling. This ensures precise paste positioning and desired board characteristics.
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 enables fine line patterning, improved conductivity, and long-term stability, allowing for the production of high-quality multilayer boards with reduced thickness and cost-effective manufacturing using general pre-preg materials, while preventing spreading and ensuring reliable stacked via structures.
Implementation Method 1
preheating the pre-preg before the drilling step to reduce the ratio of A divided by B to below 10
Implementation Method 2
at least part of the metal powder is melted and the metal powders adjacent to each other are alloyed
Implementation Method 3
using alloying paste as the conductive paste in which at least part of the metal powder is melted and the metal powders adjacent to each other are alloyed
Implementation Method 4
a drilling step for forming a via hole through a pre-preg by laser beam machining
Implementation Method 5
arranging copper layers or copper layer portions of patterned boards on and under the filled conductive paste and pressing the same
Data Source
AI summary
In a method of manufacturing a multilayer board, including: a drilling step for forming a via hole through a pre-preg by laser beam machining, a step of filling the via hole with conductive paste containing a resin component and metal powder, and a step of arranging copper layers or copper layer portions of patterned boards on and under the filled conductive paste and pressing the same, a multilayer printed wiring board superior in conductivity and long-term stability is obtained by using alloying paste as the conductive paste in which at least part of the metal powder is melted and the metal powders adjacent to each other are alloyed, using a pre-preg having a ratio A/B of at least 10 before subjected to preheating, where A is a storage modulus at an inflection point where the storage modulus changes from increasing to decreasing and B is a storage modulus at an inflection point where the storage modulus changes from decreasing to increasing in a temperature profile rising from 60° C. to 200° C., and preheating the pre-preg before the drilling step to reduce the ratio A/B to below 10.