VIPPO Solder Joint Adhesive for CTE Mismatch

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Solution Overview

Problem

The combination of VIPPO and non-VIPPO pads in printed circuit boards (PCBs) leads to mismatched coefficients of thermal expansion (CTE), causing solder joint failures known as hot tearing during the reflow process due to the differential thermal expansion between the plated metal and the PCB substrate.

Innovation Solution

Incorporating an adhesive into the PCB assembly to reduce the differential thermal expansion by applying it to the pads or components before forming the printed circuit board assembly (PCBA), which prevents solder joints from tearing during subsequent heating by distributing stresses and maintaining attachment of solder joints to both VIPPO and non-VIPPO pads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If VIPPO and non-VIPPO pads are combined in PCB to increase circuit density, then electrical interconnect performance is improved, but solder joint reliability deteriorates due to CTE mismatch causing hot tearing

Engineering Contradiction:

Improvecircuit densityVSAvoidsolder joint reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

An adhesive layer is introduced as an intermediary material between the VIPPO pad and the electronic component. This adhesive has a coefficient of thermal expansion that matches the PCB substrate, serving as a stress buffer that absorbs differential thermal expansion forces during reflow soldering, thereby preventing solder joint hot tearing while maintaining the VIPPO structure for high circuit density

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The adhesive material is specifically selected and formulated to have a coefficient of thermal expansion (CTE) that matches the PCB substrate rather than the plated metal. This parameter matching creates a gradient CTE structure where the adhesive layer absorbs the differential expansion stress between the low-CTE plated through hole and the higher-CTE PCB substrate during thermal cycling, preventing stress concentration at the solder joint

Inventive Principle:

Principle #35Parameter changes

2Reliability

If adhesive material is applied to VIPPO pads to prevent hot tearing, then solder joint reliability is improved, but manufacturing complexity increases due to additional processing steps

Engineering Contradiction:

Improvesolder joint reliabilityVSAvoidmanufacturing process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The adhesive application process is merged with the existing reflow soldering process. The adhesive is applied to the VIPPO pads before component placement, and then both the adhesive curing and solder reflow are performed in a single thermal processing step, eliminating the need for separate adhesive application equipment and reducing manufacturing complexity

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The adhesive material serves multiple functions simultaneously: it acts as a stress buffer to prevent hot tearing, provides electrical insulation, and serves as a bonding agent between the pad and component. This multi-functionality reduces the need for additional materials and process steps, offsetting the initial addition of the adhesive application step

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 adhesive reduces or eliminates hot tearing by creating a more uniform surface topology and maintaining the attachment of solder joints to both types of pads, reducing the need for additional processing steps and improving the reliability of the PCB assembly.

Implementation Method 1

mismatched coefficients of thermal expansion (CTE), causing solder joint failures known as hot tearing during the reflow process due to the differential thermal expansion between the plated metal and the PCB substrate

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

Methodology Applied

Scientific EffectAdhesive: Adhesive

Data Source

PatentUS10813228B2Preventing post reflow interconnect failures in VIPPO solder joints via utilization of adhesive material

Publication Date: 2020.10.20 INDIUM CORP

AI summary

Implementations of the disclosure describe techniques for eliminating or reducing hot tearing in via-in-pad plated over (VIPPO) solder joints by incorporating an adhesive into a printed circuit board assembly (PCBA). In an embodiment, the adhesive is an adhesive containing fluxing agent that prevents tearing by reducing a differential in thermal expansion caused by a coefficient of thermal expansion (CTE) mismatch between a plated metal of the VIPPO pads and the PCB substrate.