Thickness-Shaped IC Die Protruding Lip Delamination Resistance
Solution Overview
Problem
Conventional packaged IC devices face issues such as delamination due to differential coefficients of thermal expansion (CTE) stress, bleeding of die attach adhesive, die tilt, and moisture penetration, which affect thermal performance and reliability.
Innovation Solution
The use of thickness-shaped IC die with a protruding lip on the top portion and a varying cross-sectional area, secured to a package substrate with a die support structure having a gap region, forming a mold lock and allowing direct heat sink contact, reduces CTE-induced delamination and prevents moisture ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a solid die pad is used in conventional exposed silicon packages, then thermal performance is improved through direct heat sink contact, but delamination occurs due to differential CTE stress between the IC die and die pad
Solution Approach 1:
The die pad is segmented into an annular shape with a central opening (window), creating a die mounting ring structure. This segmentation reduces the contact area between the IC die and die pad, thereby reducing differential CTE stress and preventing delamination while maintaining thermal performance through the exposed silicon configuration.
Solution Approach 2:
The die pad structure transitions from a solid uniform design to a non-uniform annular design with different properties in different regions: the annular die pad provides mechanical support and thermal conduction, while the central opening reduces CTE stress concentration. The IC die itself is shaped with a protruding lip that concentrates the adhesive bond at specific locations rather than across the entire interface.
2Reliability
If a window pad lead frame is used to reduce contact area and prevent delamination, then delamination resistance is improved, but thermal performance deteriorates due to high thermal resistance of the epoxy-mold compound
Solution Approach 1:
The invention extracts the thermal conduction path from the epoxy-mold compound by exposing the silicon die substrate directly to the external environment. The protruding lip configuration allows heat to be dissipated directly from the silicon die to the ambient or to a heat sink, bypassing the high thermal resistance of the mold compound that would otherwise be present in conventional packages.
3Strength
If die attach adhesive is used to bond the IC die to the die pad, then mechanical bonding is achieved, but adhesive bleeding onto the top surface occurs causing bonding and reliability problems
Solution Approach 1:
The IC die is shaped with a protruding lip that creates a localized bonding region. The die attach adhesive is applied only at the interface between the protruding lip and the die pad, concentrating the bonding strength at this specific location. This localized bonding approach prevents adhesive from spreading onto the top surface of the die, thereby maintaining bonding reliability while achieving sufficient mechanical strength.
4Ease of manufacture
If conventional exposed silicon packages are used without a mold lock, then manufacturing simplicity is maintained, but ambient moisture can enter the packaged IC causing delamination and reliability problems
Solution Approach 1:
The protruding lip configuration creates a mold lock structure that prevents moisture ingress before it can reach the IC die. The lip extends into the mold compound, creating a physical barrier that seals the interface between the die pad and the mold compound, thereby preventing ambient moisture from penetrating along this interface and reaching the die, thus maintaining reliability without complicating the manufacturing process.
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 configuration enhances thermal performance by reducing delamination and moisture-related reliability issues, while maintaining effective heat transfer and preventing adhesive bleeding and die tilt.
Implementation Method 1
One type of die attach stress (generally referred to as 'differential coefficients of thermal expansion (CTE) stress') is induced by heating (or cooling) a packaged IC die that arises from forces produced by the large differential CTE between the IC die and the die mounting surface
Implementation Method 2
The bottom surface of the IC die extends below the die support structure into the gap region to form a mold lock, which in one embodiment extends sufficiently to allow the bottom surface of the substrate silicon for the thickness shaped IC die to directly contact a heat sink
Data Source
AI summary
A packaged electronic device includes a thickness shaped IC die including a top portion, top surface, active circuitry, bottom portion and bottom surface. A cross sectional area of the bottom surface is ≧5% less than a cross sectional area of the top surface to provide a protruding lip having a bottom lip surface. A package substrate includes a top substrate surface including substrate bonding sites, a bottom substrate surface, and a die support structure on the top substrate surface having a gap region. The bottom lip surface of the IC die is secured to the die support structure and the bottom surface of the IC die extends below the die support structure into the gap region. Coupling connectors couple the bonding features on the IC die to the substrate bonding sites.