Printed Wiring Board Dual-Metal Surface Layer Migration Resistance
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Solution Overview
Problem
Existing printed wiring boards face challenges in forming fine-pitch pads for mounting IC chips without compromising insulation reliability and resistance to impact, as traditional methods either fail to ensure reliable insulation or increase the risk of migration and pad detachment upon impact.
Innovation Solution
A printed wiring board design featuring a first resin insulating layer with conductor pads, a second resin insulating layer covering these pads, and an outermost surface conductor wiring layer formed from different metals (copper and nickel) with via conductors connecting them, where a solder resist layer covers the copper wiring layer and exposes the nickel wiring layer to prevent migration and enhance impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single-metal wiring layers are used, then manufacturing process is simple, but migration risk increases and impact resistance decreases
Solution Approach 1:
The patent applies composite materials by using a two-layer conductor wiring structure where a first conductor wiring layer (e.g., copper) and a second conductor wiring layer (e.g., nickel or palladium) are stacked. The first layer provides low resistance for signal transmission, while the second layer provides high impact resistance and prevents migration. This composite structure resolves the contradiction by combining materials with complementary properties to achieve both reliability and controlled complexity.
Solution Approach 2:
The patent applies local quality by making the second conductor wiring layer selectively present only in regions requiring impact resistance and migration prevention, such as under solder balls or in specific pad areas. This allows the wiring structure to have enhanced protective properties where needed while maintaining simplicity in other areas, thus resolving the contradiction between reliability improvement and device complexity.
2Manufacturing precision
If fine-pitch pads are formed with traditional methods, then mounting density increases, but insulation reliability decreases
Solution Approach 1:
The patent uses a composite resin insulating layer structure consisting of a first resin insulating layer and a second resin insulating layer with different material compositions. The second layer has superior insulation properties and is strategically positioned to provide enhanced insulation between fine-pitch pads. This composite approach enables closer pad spacing while maintaining reliable insulation, resolving the contradiction between manufacturing precision and reliability.
3Reliability
If copper is used for all wiring layers, then resistance is low, but migration risk increases upon impact
Solution Approach 1:
The patent implements a stacked conductor wiring structure where a first conductor wiring layer (copper) is combined with a second conductor wiring layer (nickel or palladium). The copper layer provides low electrical resistance for efficient signal transmission, while the nickel or palladium layer provides high impact resistance and prevents copper migration. This composite approach resolves the contradiction by combining materials with complementary electrical and mechanical properties.
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 solution allows for the formation of fine-pitch pads with reduced migration risk and increased impact resistance by using nickel for pads and copper for signal lines, achieving low resistance and cost-effectiveness while ensuring reliable insulation.
Implementation Method 1
applying electrolytic plating of a first main metal such that a first via conductor is formed in the first opening portion and a first outermost surface conductor wiring layer is formed on an exposed portion of the second resin insulating layer
Data Source
AI summary
A wiring board includes a first resin insulating layer, conductor pads on the first insulating layer including first and second conductor pads, a second resin insulating layer on the first insulating layer covering the first and second pads, an outermost conductor layer on the second insulating layer including first and second outermost wiring layers, via conductors through the second insulating layer including a first via conductor connecting the first wiring layer and first pad and a second via conductor connecting the second wiring layer and second pad, and a solder resist layer on the second insulating layer such that the solder resist layer is covering the first wiring layer and has one or more openings exposing the second wiring layer. The first wiring layer includes first main metal, and the second wiring layer includes second main metal which is different from the first metal of the first wiring layer.