Boundary Features for High Bond Line Thickness in Semiconductor Die Attach
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Solution Overview
Problem
The existing die attach processes in semiconductor manufacturing face challenges in achieving consistent bond strength and minimizing voids, which can lead to mechanical and electrical failures due to the limited bond line thickness and potential for conductive material displacement, resulting in increased stress and strain on the semiconductor device.
Innovation Solution
The use of boundary features containing bond wires on the die attach pad allows for an increased bond line thickness by containing the conductive material within a defined perimeter, preventing displacement and ensuring a robust attachment of the die to the leadframe, thereby enhancing the durability and performance of the semiconductor package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the bond line thickness is increased by using more conductive material, then the shear stress on the die is decreased, but the conductive material may flow to other portions of the leadframe or die, causing moisture paths, short circuits and wire bonding problems
Solution Approach 1:
The die attach pad is segmented into a bonding area and a non-bonding area by boundary features (such as trenches or raised structures). This segmentation confines the conductive material to the bonding area, allowing increased bond line thickness without material flow to other portions of the leadframe or die, thus preventing moisture paths, short circuits, and wire bonding problems while maintaining enhanced shear stress reduction.
Solution Approach 2:
The boundary features create local structural differences on the die attach pad, with the bonding area having properties that allow conductive material deposition and the non-bonding area having properties that prevent material flow. This local quality differentiation enables controlled material confinement and achieves both high bond strength and device reliability.
2Manufacturing precision
If a spanker is used to flatten the conductive material during die attach, then the conductive material displacement is controlled, but the device fabrication process becomes longer, less productive, and more expensive
Solution Approach 1:
Boundary features are formed on the die attach pad before the die attach process. These pre-formed features serve as physical barriers that automatically confine the conductive material during deposition, eliminating the need for subsequent spanker operations. This preliminary action achieves precise material placement while maintaining high fabrication productivity and low cost.
Solution Approach 2:
The mechanical spanker system is replaced with static boundary features (trenches or raised structures) that passively confine the conductive material through their geometric configuration. This substitution eliminates the additional mechanical flattening step, reducing process complexity, increasing productivity, and lowering manufacturing costs while maintaining precise material placement.
3Reliability
If the viscosity of the conductive material is kept low to allow effective bonding, then void formation is minimized, but the bond line thickness is limited to less than 3 mils
Solution Approach 1:
The die attach pad is divided into bonding and non-bonding areas using boundary features, creating a confined bonding area. This segmentation allows the use of low-viscosity conductive material that flows easily to fill the bonding area completely, achieving thick bond lines (greater than 3 mils) without void formation, since the material is physically constrained from flowing away during the bonding process.
Data Source
AI summary
Die attach methods used in making semiconductor devices and the semiconductor devices resulting from those methods are described. The methods include providing a leadframe with a die attach pad, using a boundary feature(s) containing a bond wire to define a perimeter on the die attach pad, depositing a conductive material (such as solder) within the perimeter, and then attaching a die containing an integrated circuit device to the die attach pad by using the conductive material. The boundary feature(s) allow an increased thickness of conductive material to be used, resulting in increased bond line thickness and increasing the durability and performance of the resulting semiconductor package. Other embodiments are described.