Semiconductor Die Attach Foam Layer for Crack-Free Lead Frames
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Solution Overview
Problem
Existing methods for connecting semiconductor dies to lead frames face challenges in stress accumulation and crack formation, particularly with larger dies, and require costly processes to manage stress relaxation, with no universal solution for all die sizes.
Innovation Solution
A semiconductor device design utilizing a metallic foam layer between the die and lead frame, interpenetrated by a second layer, creating an intermediate connection that alleviates stress and reduces dicing burrs, replacing the need for thick solid aluminum layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick solid aluminum layers are used for stress relaxation, then crack prevention is improved, but manufacturing cost increases and dicing problems occur
Solution Approach 1:
The patent replaces solid aluminum with aluminum foam material that has a porous structure. This foam material provides stress relaxation functionality while using significantly less material, thereby reducing manufacturing cost and eliminating dicing burr problems associated with thick solid aluminum layers.
Solution Approach 2:
The patent creates a composite structure by interpenetrating aluminum foam with a second metal layer (such as copper or tin). This composite material combines the stress relaxation properties of aluminum foam with the electrical conductivity and mechanical strength of the second metal, achieving crack prevention without requiring thick aluminum layers.
2Reliability
If thick solid aluminum layers are used for stress relaxation, then crack prevention is improved, but dicing quality deteriorates due to burr formation
Solution Approach 1:
The aluminum foam's porous structure allows stress relaxation without the need for thick continuous material layers. During dicing, the foam structure does not generate burrs like solid aluminum does, thereby maintaining high dicing quality while still providing crack prevention.
Solution Approach 2:
The second metal layer selectively fills only part of the aluminum foam pores, creating a structure with locally optimized properties. The foam provides stress relaxation while the localized metal interpenetration provides electrical conductivity and mechanical strength, avoiding the need for uniformly thick aluminum that causes dicing burrs.
3Ease of manufacture
If aluminum foam is used instead of solid aluminum, then manufacturing cost is reduced and dicing quality is improved, but electrical conductivity may deteriorate
Solution Approach 1:
The patent combines aluminum foam with a second metal layer (copper, tin, or their alloys) that interpenetrates the foam structure. This composite provides both the cost advantages of reduced aluminum usage and the electrical conductivity of the second metal, resolving the conductivity concern.
Solution Approach 2:
The second metal layer serves multiple functions simultaneously: it provides electrical conductivity to compensate for the lower conductivity of aluminum foam, contributes to mechanical strength, and participates in stress relaxation. This multi-functionality ensures that electrical conductivity requirements are met while maintaining the cost benefits of using aluminum foam.
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
The design enhances mechanical and thermal contact while reducing costs by using a metal foam layer, improving conductivity and preventing cracks, and eliminating the need for expensive thick aluminum layers.
Implementation Method 1
a first layer (1) comprising foam material... At least part of the second layer is interpenetrated with the first layer through the pores of the foam of the first layer
Implementation Method 2
At least part of the second layer is interpenetrated with the first layer through the pores of the foam of the first layer. This in turn creates an intermediate layer, which allows to increase the surface area of contact between first and second layer
Implementation Method 3
creates an intermediate layer, which allows to increase the surface area of contact between first and second layer, connecting them both mechanically and electrically
Implementation Method 4
it allows to alleviate stress problems replacing the solid Aluminum layer as the stress reliever
Implementation Method 5
a lead frame constituting the bottom layer of the semiconductor device, having high electrical conductivity
Implementation Method 6
a die constituting the top layer of the semiconductor device, preferably made of silicone
Data Source
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AI summary
According to a first example of the disclosure a semiconductor device is proposed, comprising a die constituting the top layer of the semiconductor device, preferably made of silicone; a lead frame constituting the bottom layer of the semiconductor device, having high electrical conductivity in the range between 6.3×107 Siemens to 1×106 Siemens more preferably 1×107 Siemens (electrical conductivity is normally measured in Siemens per meter S/m, range of conductivity for Cu alloy lead frames are between 5 to 6×107 S/m) for example made of L/F C19210 material; a first layer formed from a metallic foam located between the lead frame and the die, with a thickness preferably in the range of 500 nm to 5000 nm more preferably 2000nm, and with a porosity in range of 30% and 90% preferably 60% and a second layer located between the die and the lead frame being only partially in surface contact with the first layer.