Chip Package Lid Adhesion During Underfill Cure
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Solution Overview
Problem
Integrated circuit chip packages experience thermomechanical stresses due to thermal excursions during cooldowns, particularly high-CTE layers facing peeling stress from differential contraction with other layers.
Innovation Solution
The method involves warming the chip package to an underfill process temperature, dispensing and curing the underfill while lidding, and cooling to room temperature with the lid adhered, thereby reducing latent thermal stress in the high-CTE layer by distributing thermomechanical strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the chip package undergoes repeated thermal excursions during fabrication, then the underfill and lidding adhesives can be properly cured, but high-CTE layers experience peeling stress due to differential contraction
Solution Approach 1:
The patent combines the underfill cure process and lidding adhesive cure process into a single thermal excursion. The lidding adhesive is applied and cured simultaneously with the underfill cure, eliminating the need for separate heating cycles. This merging of processes reduces the number of thermal excursions from multiple separate cycles to one combined cycle, thereby reducing cumulative peeling stress on high-CTE layers while still achieving proper cure of both adhesives.
Solution Approach 2:
The patent applies the lidding adhesive to the lid before the thermal excursion begins, allowing it to be positioned and initially set in place. This preliminary action ensures the adhesive is ready to bond during the single thermal excursion when both underfill and lidding adhesive are cured simultaneously, rather than requiring a separate application and cure cycle after underfill completion.
2Reliability
If multiple separate thermal excursions are used for underfill cure and lidding adhesive cure, then each adhesive can be properly cured, but the cumulative thermal stress on high-CTE layers increases
Solution Approach 1:
The patent merges the underfill cure and lidding adhesive cure into one simultaneous thermal excursion. The process timeline shows both adhesives being cured during the same heated period, reducing cumulative thermal cycling from multiple separate excursions to a single excursion. This reduces the total number of heat-up and cool-down cycles, thereby minimizing cumulative peeling stress and improving structural stability while maintaining reliable cure of both adhesives.
3Reliability
If the lid is adhered after underfill cure at room temperature, then the underfill can be properly cured, but the high-CTE layer experiences maximum peeling stress during subsequent heating
Solution Approach 1:
The patent inverts the conventional sequence by adhering the lid and curing the lidding adhesive during the same thermal excursion as the underfill cure, rather than waiting for underfill cure completion at room temperature. This inversion means the lid is in place and bonded during heating, so the high-CTE layer experiences compressive or neutral stress from the bonded lid rather than peeling stress from an unbonded state, while still achieving proper underfill cure.
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 reduces residual thermal stresses and the likelihood of cooldown peeling during chip package fabrication, enhancing the stability of the lidded chip package.
Implementation Method 1
high-coefficient-of-thermal-expansion (high-CTE) chip layers experience a peeling stress due to differential contraction relative to other layers
Implementation Method 2
high-coefficient-of-thermal-expansion (high-CTE) chip layers experience a peeling stress due to differential contraction relative to other layers
Implementation Method 3
Thermal excursions introduce thermomechanical stresses to various layers of the chips
Implementation Method 4
a lid adhered to the chip and the substrate
Implementation Method 5
underfill cured between the chip and the substrate
Data Source
AI summary
A lidded chip package apparatus has reduced latent thermal stress in an under-chip high-CTE layer of the chip package because the lid of the package was adhered to a substrate of the package and cured during a same thermal excursion as when underfill was dispensed and cured under a chip of the package, and the chip package was cooled from the combined underfill and lidding process to room temperature with the lid adhered to the chip and the substrate, thereby reducing latent thermal stress in the under-chip high-CTE layer of the chip package.