Sandblasted Solder Pad Surface Roughness Prevents Bridging

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Fine pitch interconnections in electronic devices often suffer from solder bridging issues due to the limitations of existing lead-free solder technologies, which affect the reliability and yield of assembly processes such as BGA, QFP, and flip chip technologies.

Innovation Solution

A surface treatment method is applied to both the substrate and solder pads to enhance surface roughness through sandblasting, improving the wettability of pad surfaces and de-wettability of the substrate for molten solder, preventing solder bridging and enhancing the reliability and yield of solder joints.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If fine pitch interconnection is used to enhance performance, then signal transmission capability is improved, but solder bridging between adjacent solder joints occurs

Engineering Contradiction:

Improvesignal transmission capabilityVSAvoidsolder joint reliability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The invention applies different surface roughness characteristics to different regions: the pad surface is made rougher to improve solder wettability and bonding, while the substrate surface between pads is also roughened to create de-wetting barriers that prevent solder bridging. This localized differentiation of surface properties resolves the contradiction between fine pitch requirements and solder joint reliability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the surface roughness parameter (Ra) of both the pad and substrate surfaces through sandblasting treatment. By controlling the roughness parameter to be greater than 0.4 μm and lower than 2 μm, the invention modifies the wetting characteristics to prevent bridging while maintaining bonding capability, thus resolving the reliability issue in fine pitch applications.

Inventive Principle:

Principle #35Parameter changes

2Strength

If surface roughness is increased to improve solder wettability, then bonding strength is improved, but solder bridging between adjacent pads increases

Engineering Contradiction:

Improvesolder bonding strengthVSAvoidsolder joint separation

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention applies uniform surface roughness treatment to both the pad surfaces and the substrate surfaces between pads. This creates a consistent de-wetting barrier effect in the inter-pad regions while maintaining improved wettability on the pads themselves, preventing bridging without compromising bonding strength.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention converts the potential harmful effect of increased surface roughness (which could cause bridging) into a beneficial de-wetting barrier on the substrate surfaces between pads. By roughening the substrate surface, molten solder is repelled from the inter-pad regions, transforming what could be a bridging risk into a protective barrier that prevents bridging.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Ease of manufacture

If conventional smooth surfaces are used, then manufacturing process is simple, but solder bridging occurs at fine pitches

Engineering Contradiction:

Improvesurface treatment complexityVSAvoidsolder joint reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The invention replaces complex chemical surface treatment processes with a mechanical sandblasting method. This mechanical approach achieves the desired surface roughness and wetting characteristics through physical abrasion with abrasive particles, simplifying the manufacturing process while effectively preventing solder bridging at fine pitches.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 surface treatment effectively prevents solder bridging, improves the reliability of solder joints, reduces production costs, and enhances the manufacturing yield of electronic devices even at fine pitches, by modifying the wetting characteristics of the substrate and pad surfaces.

Implementation Method 1

The surface treatment includes sandblasting. The sandblasting modifies the exposed surfaces mechanically and physically without altering chemical surface condition significantly.

Methodology Applied

Scientific EffectSandblasting: Abrasion

Implementation Method 2

Application of the surface treatment, to enhance the surface roughness, improves wettability of the pad surfaces of the pads and de-wettability of the top surface of the substrate with respect to molten solder.

Methodology Applied

Scientific EffectWetting: Wetting

Implementation Method 3

Methodology Applied

Scientific EffectDe-wetting: Hydrophobe

Data Source

PatentUS11456269B2Prevention of bridging between solder joints

Publication Date: 2022.09.27 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method of fabricating a connection structure is disclosed. The method includes providing a substrate that has a top surface and includes a set of pads for soldering, each of which has a pad surface exposed from the top surface of the substrate. The method also includes applying a surface treatment to a part of the top surface of the substrate close to the pads and the pad surface of each pad so as to make at least the part of the top surface and the pad surfaces of the pads rougher. The surface treatment includes sandblasting.