Wiring Board Insulating Layer Design for Warp Reduction

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Solution Overview

Problem

Wiring boards with micro interconnect structures face manufacturing challenges due to thermal expansion mismatch between photosensitive and thermosetting resins, leading to warping and defects, and bonding issues with micro wiring boards having poor rigidity.

Innovation Solution

A wiring board design with a layered structure including a first insulating layer with no reinforcing material and a second layer with reinforcing material, both made of non-photosensitive thermosetting resin, and a photosensitive resin layer, which helps in reducing thermal expansion mismatch and increasing rigidity, thereby minimizing warp and improving bonding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a micro interconnect structure is formed on a base board using photosensitive resin, then high interconnect density is achieved, but warping occurs due to thermal expansion mismatch between photosensitive and thermosetting resins

Engineering Contradiction:

Improveinterconnect densityVSAvoidwarp

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The insulating layer is divided into two separate layers: a first insulating layer made of thermosetting resin and a second insulating layer made of photosensitive resin. This segmentation allows each layer to have optimized properties - the first layer provides dimensional stability and low thermal expansion, while the second layer enables high interconnect density through photolithography processes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses a composite structure combining two different resin materials (thermosetting resin and photosensitive resin) in separate layers. This composite approach leverages the advantages of each material - the thermosetting resin's dimensional stability and the photosensitive resin's patterning capability - while mitigating their individual disadvantages through proper layer configuration.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If the base board and micro wiring board are manufactured separately and bonded, then high interconnect density is achieved, but bonding becomes difficult due to poor rigidity of the micro wiring board

Engineering Contradiction:

Improveinterconnect densityVSAvoidrigidity

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The patent merges the formation of the micro interconnect structure with the base board manufacturing process by forming the high-density interconnect layer on the first insulating layer before final board completion. This integration ensures the micro wiring board maintains sufficient rigidity throughout the manufacturing process, enabling reliable bonding while achieving high interconnect density.

Inventive Principle:

Principle #5Merging (Combining)

3Manufacturing precision

If photosensitive resin is used for the interconnect layer, then high interconnect density is achieved, but manufacturing waste increases due to process sequence constraints

Engineering Contradiction:

Improveinterconnect densityVSAvoidmanufacturing waste

Core Design Contradiction:

Manufacturing precisionVSLoss of substance

Solution Approach 1:

The first insulating layer made of thermosetting resin is prepared in advance with controlled thermal expansion properties. This preliminary action establishes a stable foundation that prevents warping during subsequent photosensitive resin processing, ensuring high interconnect density can be achieved without requiring excessive material compensation or rework.

Inventive Principle:

Principle #10Preliminary action

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 design achieves a wiring board with high interconnect density, high rigidity, and reduced warp, enhancing manufacturing efficiency and bonding reliability.

Implementation Method 1

the first layer has a coefficient of thermal expansion higher than a coefficient of thermal expansion of the second layer

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

the curing temperature of the photosensitive resin is higher than the curing temperature of the thermosetting resin

Methodology Applied

Scientific EffectCuring: Photopolymerisation

Data Source

PatentUS10905005B2Wiring board, laminated wiring board, and semiconductor device

Publication Date: 2021.01.26 SHINKO ELECTRIC IND CO LTD

AI summary

A wiring board includes a first interconnect layer, a first insulating layer covering the first interconnect layer, a second interconnect layer, thinner than the first interconnect layer, formed on the first insulating layer and having an interconnect density higher than that of the first interconnect layer, and a second insulating layer formed on the first insulating layer and covering the second interconnect layer. The first insulating layer includes a first layer including no reinforcing material, and a second layer including a reinforcing material. The first and second layers include a non-photosensitive thermosetting resin as a main component thereof. The first layer has a coefficient of thermal expansion higher than that of the second layer, and the second insulating layer includes a photosensitive resin as a main component thereof. The second interconnect layer includes an interconnect formed directly on and electrically connected to the first interconnect layer.