Solder Array Thermal Interface for Void-Resistant Chip Packaging

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Solution Overview

Problem

Conventional solder TIM (STIM) used in microelectronic packages melts and flows out during BGA solder ball attach or board assembly processes, leading to voids and degraded thermal performance, and further degrades due to temperature cycling and stress in the solder material.

Innovation Solution

The use of a solder array TIM (SA-TIM) with an array of solder contacts mechanically protected by polymer underfill material, reducing the z-height of the STIM layer to less than 150 microns, thereby preventing squeeze-out or flow-out during assembly and accommodating chip height variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional solder TIM (STIM) is used to attach IHS to silicon die, then thermal performance is improved, but the solder TIM melts and flows out during BGA solder ball attach or board assembly processes, leading to voids and degraded thermal performance

Engineering Contradiction:

Improvethermal performanceVSAvoidstructural integrity of STIM

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The solder TIM is segmented into an array of discrete solder contacts rather than a continuous layer. This segmentation prevents the solder from flowing out as a continuous mass during reflow, while each individual solder contact maintains its structural integrity. The segmented array configuration allows the solder to remain stable during BGA assembly processes while still providing effective thermal conduction paths.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite structure combining solder material with a polymer underfill matrix. The solder contacts are embedded in or surrounded by the polymer underfill material, creating a composite TIM structure. This composite approach provides the thermal conductivity of solder while the polymer matrix prevents flow-out and provides mechanical stability during assembly and temperature cycling.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If the z-height of STIM layer is reduced to prevent squeeze-out during assembly, then manufacturing precision is improved, but thermal performance may be degraded due to thinner thermal conduction path

Engineering Contradiction:

Improvecontrol of STIM layer thicknessVSAvoidthermal performance

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

By segmenting the TIM into discrete solder contacts with controlled z-height, the invention achieves precise thickness control without compromising thermal performance. Each solder contact can be individually sized to optimize thermal conduction while maintaining a thin overall profile that prevents squeeze-out during assembly. The segmented structure allows for better manufacturing control compared to a continuous TIM layer.

Inventive Principle:

Principle #1Segmentation

3Reliability

If conventional STIM is used, then thermal performance is improved, but the STIM degrades due to temperature cycling and stress in the solder material

Engineering Contradiction:

Improvethermal performanceVSAvoidservice life under temperature cycling

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The composite structure of solder contacts embedded in polymer underfill provides enhanced resistance to temperature cycling and mechanical stress. The polymer matrix has better thermal expansion matching with the surrounding materials, reducing stress on the solder joints during thermal cycling. This composite approach extends the service life of the TIM while maintaining thermal performance.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The polymer underfill material acts as a cushioning matrix that protects the solder contacts from excessive mechanical stress and thermal shock. This protective environment prevents premature degradation of the solder material during temperature cycling, extending the operational life of the TIM assembly.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 SA-TIM provides improved thermal performance by preventing void formation and maintaining structural integrity under temperature cycling, while allowing for thinner bond lines and better accommodation of chip height variations.

Implementation Method 1

an array of solder contacts mechanically protected by polymer underfill material

Methodology Applied

Scientific EffectMechanical protection:

Implementation Method 2

The SA-TIM provides improved thermal performance by preventing void formation and maintaining structural integrity

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS12205915B2Microelectronic package with solder array thermal interface material (SA-TIM)

Publication Date: 2025.01.21 INTEL CORP

AI summary

Embodiments may relate to a microelectronic package that includes a die coupled with a package substrate. A plurality of solder thermal interface material (STIM) thermal interconnects may be coupled with the die and an integrated heat spreader (IHS) may be coupled with the plurality of STIM thermal interconnects. A thermal underfill material may be positioned between the IHS and the die such that the thermal underfill material at least partially surrounds the plurality of STIM thermal interconnects. Other embodiments may be described or claimed.