Leadframe Fillister for Thermal Conduction and Inspection Reliability
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Solution Overview
Problem
Conventional semiconductor packages with exposed die paddles face issues during thermal cycling, leading to irregular protrusions of solder plating material, which can cause visual inspection failures and electrical shorts due to contact with underlying circuitry or bond fingers, resulting in rejected packages.
Innovation Solution
The solution involves recessing the back side of the die paddle or providing a fillister on the exposed back side of the die paddle, ensuring the plating material's protrusions are accommodated within the recess, preventing contact with the support's underlying features during surface mounting, thereby reducing the risk of electrical shorts and improving visual inspection pass rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder plating material is applied on the exposed back side of the die paddle, then thermal conduction from the package to the support is improved, but irregular protrusions of the plating material occur during thermal cycling, causing visual inspection failures and electrical shorts
Solution Approach 1:
The patent applies different surface treatments to different regions of the die paddle. The back side of the die paddle is coated with solder plating material to enhance thermal conduction, while the front side maintains its original finish for proper die attachment. This localized application of solder plating ensures thermal management benefits without compromising visual inspection or creating harmful protrusions on the functional surfaces.
Solution Approach 2:
The solder plating material is applied to the back side of the die paddle during the manufacturing process, before the package undergoes thermal cycling and before mounting on the support. This preliminary coating ensures that the thermal conduction path is established in advance, and the plating material is already in position to accommodate any subsequent thermal expansion or cycling without creating harmful protrusions that would cause inspection failures or electrical shorts.
2Reliability
If solder plating material is applied on the exposed back side of the die paddle, then thermal conduction from the package to the support is improved, but the protrusions of plating material contact underlying circuitry or bond fingers, causing electrical shorts
Solution Approach 1:
The solder plating material is selectively applied only to the back side of the die paddle, which is the region that contacts the support for thermal conduction. This localized coating avoids applying plating material on the front side or edges where protrusions could contact underlying circuitry or bond fingers, thus preventing electrical shorts while maintaining thermal conduction benefits.
Solution Approach 2:
The patent acknowledges that solder plating material can create harmful protrusions during thermal cycling, but converts this potential harm into a benefit by strategically placing the plating material on the back side of the die paddle. The protrusions that would normally cause electrical shorts are instead directed toward the support, where they enhance thermal conduction. This transforms the harmful protrusion effect into a beneficial thermal management feature.
3Reliability
If the die paddle is recessed or a fillister is provided, then protrusions of plating material are accommodated preventing contact with support features, but the manufacturing process becomes more complex
Solution Approach 1:
Instead of recessing the entire die paddle or adding complex fillister structures, the patent applies solder plating material locally only to the back side of the die paddle. This localized coating approach achieves the same effect of accommodating protrusions and preventing electrical shorts, but with a simpler manufacturing process that avoids the complexity of mechanical recessing or fillister formation.
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 design enhances the likelihood of passing visual inspection and achieving reliable electrical connections by reducing vertical offset and preventing unwanted contact with circuitry, leading to more reliable surface mounts and improved solder joint durability.
Implementation Method 1
applying heat to reflow the solder and complete the connection
Implementation Method 2
heat is conducted from the back side of the die, through the adhesive, to the die paddle
Implementation Method 3
thermally conductive vias carry heat from the thermal pad to the opposite side of the support, or to a thermally conductive layer
Data Source
AI summary
A leadframe includes a die paddle and leads, in which the back side of the die paddle has a fillister. The fillister defines a rim surrounding a recess, and the recess accommodates protrusion of fusible material. Also, a package includes such a leadframe. Also, a method for making a leadframe includes patterning a sheet of metal to form a die paddle and leads, and forming a fillister in the back side of the die paddle.