IC Chip Assembly Pre-Stress Curing for Warpage Control
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Solution Overview
Problem
Conventional electronic packages using ceramic or organic substrates face significant warpage and stress issues due to thermal expansion mismatches, leading to reduced lifespan and assembly quality, with existing methods only able to minimize warpage-induced stresses by 50% at best.
Innovation Solution
Introducing a pre-stress during the cure process by constraining the substrate within a tub-like tray, allowing controlled expansion and contraction, thereby reducing residual warpage and peak stress, and adjusting the neutral temperature point to manage warpage-free conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an organic substrate is used to reduce cost, then manufacturing cost is reduced, but warpage and stress increase due to CTE mismatch
Solution Approach 1:
A balance plate is pre-installed on the organic substrate before die attachment. The balance plate has a CTE specifically designed to counteract the CTE mismatch between the organic substrate and silicon die, thereby preemptively compensating for thermal expansion differences and reducing warpage and stress during temperature cycling.
Solution Approach 2:
The patent employs a composite structure consisting of the organic substrate, balance plate, and silicon die. The balance plate acts as an intermediate layer with tailored mechanical and thermal properties, creating a composite system that harmonizes the CTE differences between the organic substrate and silicon die, thereby reducing overall warpage and stress.
2Stability of the object's composition
If a balance plate is added to counteract warpage, then warpage-induced stress is reduced, but device complexity increases
Solution Approach 1:
The balance plate serves multiple functions simultaneously: it provides mechanical support for die attachment, compensates for CTE mismatch between organic substrate and silicon die, and counteracts warpage during thermal cycling. By consolidating these functions into a single component, the patent reduces overall device complexity while achieving stress reduction.
3Reliability
If underfill material is used to relieve C4 stress, then C4 connection reliability improves, but die stress increases due to high elastic modulus
Solution Approach 1:
The balance plate is installed before die attachment and underfill application. It pre-establishes a mechanically stable platform that compensates for CTE mismatch, thereby reducing the burden on the underfill material and minimizing stress transmission to the die during subsequent assembly and thermal cycling.
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 warpage-induced stresses by 50% and extends the life cycle of the assembly by halving peak stress, allowing for better control over warpage and stress levels within acceptable industry limits.
Implementation Method 1
The coefficient of thermal expansion (CTE) for both the silicon die and the ceramic are close enough (about 3 ppm/° C.) that temperature excursions do produce comparable elongation of these elements. However, any difference in CTE subject to a change in temperature could produce shear and other forms of stresses in the solder ball connections
Implementation Method 2
The temperature excursion of Tg=125° C. to Troom=25° C. causes an assembly to warp as much as 150 μm on a 50×50 mm square substrate supporting a 20×20 mm die. This warpage is unidirectional (i.e., the die/substrate assembly goes from a planar shape to a concave system (as viewed from the die side))
Data Source
AI summary
A method (and apparatus) of assembling a die on an electronic substrate, includes processing an assembly including a substrate and a die, and during the processing, introducing a pre-stress to the assembly during a cure process.