Lid Attach Process Using Indium Reflow and Adhesive Curing

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Solution Overview

Problem

Conventional methods for attaching a lid to an integrated circuit package face challenges in achieving uniform thermal interface material thickness and heat transfer due to lid tilt and thermally-induced adhesive movement, particularly with indium as the thermal interface material.

Innovation Solution

A method involving the application of an adhesive to the substrate, an indium film to the integrated circuit or lid, partial hardening of the adhesive, reflowing the indium film without compressive force, and final curing to establish a metallurgical bond between the integrated circuit, indium, and lid, while maintaining lid tilt tolerances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If adhesive is applied and lid is attached before indium reflow, then lid positioning is established, but thermally-induced adhesive movement causes tilt and nonuniform thermal interface material thickness

Engineering Contradiction:

Improvelid tilt toleranceVSAvoidmetallurgical bond consistency

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The adhesive is applied and the lid is positioned on the substrate before the indium reflow process. This preliminary positioning establishes the lid tilt geometry early in the process, allowing subsequent reflow to occur with the lid already in its final positional relationship to the substrate and integrated circuit.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The process utilizes controlled temperature changes during the reflow operation to melt and redistribute the indium thermal interface material. By heating to the indium melting point and maintaining temperature, the indium flows to fill gaps and create uniform thickness between the lid and integrated circuit, then cools to form a consistent metallurgical bond.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If indium is used as thermal interface material, then thermal resistance uniformity is improved, but achieving consistent wetting and metallurgical bonding becomes difficult

Engineering Contradiction:

Improvethermal resistance uniformityVSAvoidindium wetting control

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The indium thermal interface material undergoes a phase transition from solid to liquid during the reflow process. By heating to the indium melting point, the material becomes liquid and flows to wet the surfaces of the integrated circuit and lid, filling voids and creating uniform thickness. Upon cooling, the indium solidifies to form a consistent metallurgical bond with uniform thermal resistance.

Inventive Principle:

Principle #36Phase transitions

Solution Approach 2:

The reflow process acts as an intermediary mechanism that facilitates indium wetting. The controlled heating environment enables the indium to reach its melting point and flow across the interface between the integrated circuit and lid, creating reliable metallurgical bonds without requiring complex surface preparation or application techniques.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If adhesive curing is performed during indium reflow, then process time is reduced, but lid tilt may change due to thermal movement

Engineering Contradiction:

Improveprocess cycle timeVSAvoidlid tilt tolerance

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The adhesive curing process is merged with the indium reflow process by performing both operations during the same heating cycle. The temperature profile used to melt and redistribute the indium also serves to cure the adhesive, eliminating the need for separate curing steps and reducing overall process time while maintaining lid positioning stability.

Inventive Principle:

Principle #5Merging (Combining)

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 ensures consistent metallurgical bonding and uniform thermal resistance, improving heat transfer characteristics by maintaining lid tilt and preventing nonuniformities in thermal interface material thickness.

Implementation Method 1

A consistent metallurgical bond between the integrated circuit and the indium, and in turn, between the indium and the package lid is desirable

Methodology Applied

Scientific EffectMetallurgical bonding: Welding

Implementation Method 2

the indium film is reflowed

Methodology Applied

Scientific EffectReflow: Melting

Implementation Method 3

An adhesive is applied to the substrate and an indium film is applied to the integrated circuit. The lid is positioned on the adhesive. The adhesive is partially hardened and the indium film is reflowed. The adhesive is cured.

Methodology Applied

Scientific EffectAdhesive bonding: Adhesive

Data Source

PatentUS8865527B2Lid attach process

Publication Date: 2014.10.21 ONESTA IP LLC

AI summary

Various methods of attaching a lid to an integrated circuit substrate are provided. In one aspect, a method of attaching a lid to a substrate that has an integrated circuit positioned thereon is provided. An adhesive is applied to the substrate and an indium film is applied to the integrated circuit. The lid is positioned on the adhesive. The adhesive is partially hardened and the indium film is reflowed. The adhesive is cured.