Temperature-Controlled Underfill Flow for Void-Free Flip-Chip Assembly
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Solution Overview
Problem
The existing methods for underfilling in flip-chip electronic assemblies often result in voids and mechanical stress due to the coefficient of thermal expansion difference between semiconductor materials and substrates, leading to potential assembly failure.
Innovation Solution
A method and apparatus that control the capillary flow of a temperature-dependent polymer precursor to fill the gap between the chip and substrate without voids, using a heatable plate with temperature zones and movable capillaries to manage viscosity and ensure a linear front of polymer flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the underfill is dispensed and pulled into the gap by capillary forces at room temperature, then the precursor flows into the gap, but voids form and the filler clusters due to uncontrolled viscosity
Solution Approach 1:
The patent applies temperature control to change the viscosity parameter of the polymer precursor. By heating the precursor to a controlled temperature range, the viscosity is reduced to allow smooth capillary flow without void formation. The temperature is then reduced to allow proper curing, thus resolving the contradiction between achieving void-free filling and ensuring assembly reliability.
Solution Approach 2:
The patent performs preliminary heating of the polymer precursor before dispensing it into the gap. This preliminary temperature control ensures that the precursor has the optimal viscosity for capillary flow before the underfilling process begins, preventing void formation and filler clustering from the outset.
2Productivity
If the number of bump interconnections increases and bump size shrinks, then the electrical connection capability improves, but the number of voids in the underfill and filler clustering increase sharply
Solution Approach 1:
The patent changes the temperature parameter of the polymer precursor to control its viscosity during underfilling. This allows the precursor to flow smoothly into gaps with high bump density without forming voids or allowing filler clustering, thus resolving the contradiction between increased bump interconnection density and reduced void content.
3Adaptability or versatility
If the CTE difference between semiconductor material and substrate is large, then the material selection flexibility improves, but mechanical stresses are created during thermal cycling
Solution Approach 1:
The patent changes the temperature parameter during the underfilling process to control polymer precursor viscosity and flow characteristics. The controlled temperature profile ensures complete gap filling before curing, creating a stress-compensating underfill structure that reduces mechanical stress on solder bumps during thermal cycling, thus resolving the contradiction between material selection flexibility and mechanical stress.
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 provides a void-free and stress-free underfilling process, enhancing the reliability of semiconductor devices by maintaining the electrical connection and reducing the risk of assembly failure, applicable to large-chip products with fine bump pitches and various material combinations.
Implementation Method 1
A quantity of the precursor is deposited at a chip side and pulled into the gap by capillary action.
Implementation Method 2
A polymer precursor is selected for its viscosity of known temperature dependence. The capillary flow is controlled by controlling the viscosity based on the temperature profile.
Implementation Method 3
Thereafter, the precursor is heated, polymerized and 'cured' to form an encapsulant.
Data Source
AI summary
A method and apparatus for assembling a semiconductor device. A chip (901) with solder bodies (903) on its contact pads is flipped onto a substrate (904). After the reflow process, a gap (910) spaces chip and substrate apart. A polymer precursor is selected for its viscosity of known temperature dependence. The apparatus has a plate (800) with heating and cooling means to select and control a temperature profile from location to location across the plate. After preheating, the assembly is placed on a mesa (801) of the plate configured to heat only a portion of the substrate. Movable capillaries (840, 921) blow cooled gas onto selected locations of the assembly. After the temperature profile is reached, a quantity of the precursor is deposited at a chip side and pulled into the gap by capillary action. The capillary flow is controlled by controlling the precursor viscosity based on the temperature profile, resulting in a substantially linear front, until the gap is filled substantially without voids.