Solder Resist Opening Depth for Solder Bump Formation

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Solution Overview

Problem

Conventional methods for manufacturing printed wiring boards with solder bumps face issues such as deformation and unevenness of solder balls due to the use of a squeegee, leading to lower product quality, and struggle with achieving high-height solder bumps on small-diameter connection pads, which can result in incomplete connections and stress between IC chips and printed wiring boards.

Innovation Solution

A method involving the formation of a solder resist layer with specific openings that expose connection pads, loading solder balls into these openings, and forming bumps by reflow, where the depth of the openings is optimized between 3 μm to 18 μm to ensure reliable connection and prevent deformation or sticking, using a suction-based apparatus to accurately place solder balls without damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a squeegee is used to load solder balls on connection pads, then the solder balls can be placed on the pads, but the solder balls become deformed and uneven, leading to lower product quality

Engineering Contradiction:

Improvesolder ball loading efficiencyVSAvoidsolder ball uniformity

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent extracts the harmful squeegee component from the solder ball loading process and replaces it with a suction-based placement apparatus. This removes the mechanical deformation caused by the squeegee while maintaining efficient loading capability through vacuum suction and precise positioning.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical squeegee-based loading system with a suction-based system using vacuum pressure. This substitution eliminates the mechanical contact that causes deformation, using instead a non-contact suction method to pick up and place solder balls precisely on connection pads.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If solder balls are loaded on small-diameter connection pads, then electrical connection is achieved, but the solder bumps are insufficient in height, resulting in incomplete connections and stress between IC chips and printed wiring boards

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidsolder bump height

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The patent changes the depth parameter of the opening in the solder resist layer to optimize solder bump height. By adjusting the opening depth to expose more of the connection pad while maintaining proper solder ball placement, the solder bumps achieve sufficient height for reliable connections without causing stress issues.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If the opening depth in solder resist layer is increased to allow solder ball placement, then solder balls can be loaded, but solder balls may get stuck on the upper edge face of the opening

Engineering Contradiction:

Improvesolder ball loading easeVSAvoidsolder ball placement reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent optimizes the depth parameter of the opening in the solder resist layer. By setting the depth within a specific range that exposes the connection pad while maintaining appropriate clearance, the design prevents solder balls from getting stuck on the upper edge while still allowing easy loading and reliable placement.

Inventive Principle:

Principle #35Parameter changes

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 method ensures the formation of high-height solder bumps on small-diameter connection pads with improved reliability and uniformity, reducing the risk of incomplete connections and stress between IC chips and printed wiring boards, while minimizing damage to solder balls during the loading process.

Implementation Method 1

using a suction-based apparatus to accurately place solder balls without damage

Methodology Applied

Scientific EffectSuction: Suction

Implementation Method 2

forming a bump on the exposed connection pad by heating the solder ball to a reflow temperature

Methodology Applied

Scientific EffectHeating: Heating

Data Source

PatentUS8083123B2Method for manufacturing a printed wiring board

Publication Date: 2011.12.27 IBIDEN CO LTD

AI summary

A method of manufacturing a printed wiring board having at least one solder bump includes forming a solder resist layer on a conductor layer. The solder resist layer has at least one opening that exposes a connection pad of the conductor layer, and the at least one opening in the solder resist layer has a depth D, from the solder resist layer to the exposed connection pad, of from 3 μm to 18 μm. The method also includes loading a solder ball into each of the at least one opening in the solder resist layer, and forming a bump on the exposed connection pad by heating the solder ball to a reflow temperature.