Substrate Pre-Curvature Curing to Reduce Post-Cure Warpage
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Solution Overview
Problem
Warped substrates due to non-uniform thermal expansion and contraction rates during processing lead to delays and inefficiencies in substrate processing, as conventional thermal processes often result in substrates being processed near the thermoplastic regime, causing excessive warpage beyond acceptable levels.
Innovation Solution
The method involves applying an epoxy mold over dies on a substrate, placing it on a pedestal with a curvature opposite to its expected post-cure deflection, and curing it in a controlled heating environment to induce a controlled curvature, typically elevating the central region by 1 to 3 mm relative to the outer edge, using a curing chamber with a heat source set between 100 to 200 degrees Celsius.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thermal processes are used to cure substrates, then the substrate can be cured effectively, but the substrate develops warpage due to non-uniform thermal expansion and contraction
Solution Approach 1:
The substrate is pre-curved in the opposite direction of the expected warpage before curing. This preliminary action creates a pre-stress state that counteracts the thermal expansion and contraction forces during curing, allowing the substrate to remain flat after the thermal process completes.
Solution Approach 2:
The patent modifies the physical state and stress parameters of the substrate by applying controlled curvature and pre-stress before the thermal curing process. This parameter change enables the substrate to compensate for thermal effects and maintain flatness throughout the curing process.
2Reliability
If the substrate is processed near the thermoplastic regime to ensure proper curing, then the epoxy mold compound flows and cures effectively, but excessive warpage occurs beyond acceptable levels
Solution Approach 1:
The substrate is pre-curved before entering the thermoplastic regime during curing. This preliminary action ensures that when the epoxy mold compound flows and cures at elevated temperatures, the pre-existing curvature compensates for the thermal effects, maintaining substrate flatness even while processing through the thermoplastic regime.
3Manufacturing precision
If uniform thermal expansion and contraction are achieved, then substrate warpage is reduced, but this requires precise control of heating and cooling rates which increases process complexity
Solution Approach 1:
Instead of relying on complex thermal control to achieve uniform expansion and contraction, the patent applies a simple pre-curving action before curing. This preliminary geometric modification allows the substrate to naturally compensate for thermal effects during standard heating and cooling cycles, reducing the need for sophisticated thermal control systems.
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 effectively reduces substrate warpage, preventing damage and increasing production yields by prestressing the substrate before curing, thus ensuring it meets the stringent requirements for downstream processes like semiconductor back-end-of-line packaging.
Implementation Method 1
curing the substrate by heating the substrate in the curing chamber
Implementation Method 2
inducing a curvature on the substrate so that a central region of the substrate is elevated about 1 to about 3 mm with respect to an outer edge of the substrate
Implementation Method 3
non-uniform expansion/contraction rates in current process equipment
Implementation Method 4
non-uniform cooling and, subsequently, contraction rates give rise to a warped substrate
Data Source
AI summary
Embodiments of methods and apparatus for reducing warpage of a substrate are provided herein. In some embodiments, a method for reducing warpage of a substrate includes: applying an epoxy mold over a plurality of dies on the substrate in a dispenser tool; placing the substrate on a pedestal in a curing chamber, wherein the substrate has an expected post-cure deflection in a first direction; inducing a curvature on the substrate in a direction opposite the first direction; and curing the substrate by heating the substrate in the curing chamber.