Flame Retardant Multilayer PCB With High Conductive Surface Area
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Solution Overview
Problem
Existing multi-layer printed circuit boards face challenges in meeting flame resistance and smoke suppression requirements, particularly in the aviation industry, due to their high proportion of combustible non-conductive materials, which can lead to incomplete destruction and excessive smoke development during tests.
Innovation Solution
A multi-layer printed circuit board design featuring interconnected layers of non-combustible conductive material with a high surface proportion, separated by non-conductive material, and an additional soldering mask on the conductive layers, ensuring a high volume fraction of non-combustible conductive material and controlled thickness of non-conductive layers to minimize smoke and enhance flame resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional multilayer PCB designs with high proportion of non-conductive materials are used, then manufacturing ease and typical electrical functionality are maintained, but flame resistance and smoke suppression performance deteriorate
Solution Approach 1:
The PCB is divided into multiple layers with alternating conductive and non-conductive materials. Each layer has specific thickness requirements (conductive layers < non-conductive layers) and surface area requirements (at least 50% conductive material in interior layers). This segmentation allows the structure to meet flame resistance standards while maintaining manufacturability through standardized layering processes.
Solution Approach 2:
The invention uses composite construction combining non-combustible conductive materials (such as metal foils or mesh) with non-conductive materials (such as fiberglass or polymer substrates). This composite approach enables the PCB to achieve both electrical functionality and flame resistance, meeting the smoke density test requirement of Dm < 200 while maintaining structural integrity.
2Reliability
If the surface area of non-combustible conductive material is increased to meet smoke density test requirements, then flame resistance improves, but the proportion of non-conductive material decreases potentially affecting insulation performance
Solution Approach 1:
Different layers have different conductive material surface area requirements. Interior layers require at least 50% conductive material surface area for smoke suppression, while outer layers require at least 15%. The non-conductive material thickness is controlled to be greater than conductive layer thickness, ensuring adequate insulation. This local quality differentiation meets both smoke density test requirements and electrical insulation needs.
3Object-generated harmful factors
If the thickness of non-conductive layers is reduced to increase conductive material proportion, then smoke development is reduced, but mechanical strength and handling durability deteriorate
Solution Approach 1:
The invention specifies precise parameter ranges: non-conductive layer thickness must be greater than conductive layer thickness, and non-conductive layer thickness must be at most 250 μm. These parameter constraints optimize the balance between smoke suppression (reduced combustible material) and mechanical strength (adequate layer thickness). The volume fraction of conductive material is required to be at least 8%, ensuring sufficient smoke suppression performance.
Data Source
Figure 1~2
AI summary
In the case of a multilayered printed circuit board (20), more particularly a flame‑resistant and/or smoke‑suppressing multilayered printed circuit board, consisting of a plurality of interconnected layers (2, 3, 12, 13) composed of incombustible, conductive material and layers (1, 11) composed of non‑conductive material, two layers (2, 3, 12) composed of a conductive material in each case being separated by at least one layer (1, 11) composed of a non‑conductive material, it is provided that the printed circuit board (20) contains in its interior at least two layers (2, 3, 12) having a surface proportion of at least 50%, more particularly at least 70%, composed of the incombustible, conductive material, as a result of which a multilayered printed circuit board (20) having improved flame resistance and reduced smoke evolution can be made available.