Printed Wiring Board High-Density Bump Formation

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Solution Overview

Problem

Existing printed wiring boards face challenges in forming metal posts of different sizes at high densities due to difficulties in forming openings in the solder resist layer, leading to reduced productivity and lower density of bumps.

Innovation Solution

A printed wiring board design featuring a base insulating layer with conductor pads of varying diameters, where bumps are formed with base and top plating layers, with embedded and exposed portions of equal diameters, allowing for high-density bump formation without the need for sequential laser opening of solder resist for each bump, and a manufacturing method involving dry film resist layer formation, metal plating, and plasma treatment to position top plating layers outside the solder resist.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If sequential laser opening of solder resist is performed for each bump, then precise opening formation is achieved, but productivity decreases and manufacturing time increases

Engineering Contradiction:

Improveopening formation precisionVSAvoidbump formation productivity

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

Multiple individual laser opening operations are merged into a single simultaneous opening formation step. The patent forms openings for multiple bumps of different sizes at the same time using one opening operation, eliminating the need for sequential processing and significantly improving productivity while maintaining precision through the unified opening formation process

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The solder resist layer is designed with pre-determined opening patterns that accommodate multiple bumps of different sizes. The opening formation is performed in advance as a single step before bump formation, allowing subsequent bump processing to proceed efficiently without repeated opening operations

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If bumps of different sizes are formed on conductor pads of different sizes, then design flexibility is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvebump size adaptabilityVSAvoidmanufacturing process complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies different bump sizes and plating configurations to specific local regions (conductor pads) based on their functional requirements. Each conductor pad receives a bump size appropriate to its function, achieving design flexibility while the unified opening formation process keeps manufacturing complexity manageable

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention varies bump parameters (diameter, height, plating thickness) according to the specific requirements of different conductor pads. By changing these parameters locally rather than using a uniform approach, the patent achieves adaptability for different applications while maintaining a relatively simple overall manufacturing process

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If the exposed portion diameter of bumps is larger than the embedded portion diameter, then bump formation is simplified, but bump density decreases

Engineering Contradiction:

Improvebump formation easeVSAvoidbump density

Core Design Contradiction:

Ease of manufactureVSQuantity of substance

Solution Approach 1:

The patent intentionally creates an asymmetric relationship between embedded and exposed portion diameters, with the exposed portion being smaller than or equal to the embedded portion. This asymmetric design allows bumps to be positioned closer together, increasing bump density while remaining manufacturable through controlled plating processes

Inventive Principle:

Principle #4Asymmetry

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 the formation of high-density bumps with improved productivity by eliminating the need for sequential laser opening of solder resist, ensuring equal diameters for embedded and exposed portions of bumps, thus enhancing bump density and manufacturing efficiency.

Implementation Method 1

plasma treatment to position top plating layers outside the solder resist

Methodology Applied

Scientific EffectPlasma treatment: Plasma

Implementation Method 2

applying first metal plating such that a first base plating layer is formed on the first conductor pad and applying second metal plating such that a first top plating layer is formed on the first base plating layer

Methodology Applied

Scientific EffectMetal plating: Electroplating

Data Source

PatentUS11019732B2Printed wiring board and method for manufacturing the same

Publication Date: 2021.05.25 IBIDEN CO LTD

AI summary

A printed wiring board includes an insulating layer, a conductor layer formed on the insulating layer and including first and second pads, a solder resist layer formed on the insulating layer, covering the conductor layer and exposing the first and second pads to form the second pad having diameter smaller than diameter of the first pad, a first bump formed on the first pad and including first base and top plating layers such that the first base layer has embedded portion in the resist layer and exposed portion and having diameter substantially equal to or smaller than diameter of the embedded portion, and a second bump formed on the second pad and including second base and top plating layers such that the second base layer has embedded portion in the resist layer and exposed portion and having diameter substantially equal to or smaller than diameter of the embedded portion.