Semiconductor Leadframe Back Etching for Creepage Distance
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Solution Overview
Problem
Existing methods to increase creepage distance between solder joints in semiconductor devices, such as those used in automotive applications, incur additional costs and lead-time issues due to customized leadframe and substrate layouts, and are prone to insulating material damage during handling and assembly.
Innovation Solution
A method involving laser ablation to selectively remove a masking layer from electrically conductive leads, followed by back etching to expose and remove undesired leads, thereby increasing creepage distance without altering the overall assembly process significantly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If custom leadframe and substrate layouts are used to increase creepage distance, then creepage distance is improved, but manufacturing cost and lead time increase
Solution Approach 1:
The patent applies preliminary action by pre-plating the entire substrate surface with a masking layer (such as nickel, palladium, or gold) before leadframe attachment. This pre-prepared masking layer enables selective lead removal through laser ablation without requiring custom leadframe designs, thereby achieving increased creepage distance while maintaining standard manufacturing processes and cost structures.
2Reliability
If insulating material is applied to electrically conductive leads to increase creepage distance, then creepage distance is improved, but the insulating material is susceptible to damage during handling and assembly
Solution Approach 1:
The patent inverts the conventional approach by removing unwanted electrically conductive leads through selective laser ablation of the masking layer instead of adding insulating material to protect leads. This eliminates the vulnerability of insulating materials to mechanical damage during handling while achieving the same creepage distance enhancement through selective lead removal.
3Reliability
If selective lead removal is performed to increase creepage distance, then creepage distance is improved, but additional manufacturing steps are required
Solution Approach 1:
The patent replaces mechanical leadframe customization with a laser-based ablation process. The selective removal of leads is achieved through laser ablation of the pre-plated masking layer, which is controlled by digital patterns. This substitution of mechanical customization with a programmable laser process adds minimal complexity while enabling flexible creepage distance adjustment without custom tooling.
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
Enhances creepage distance effectively while minimizing additional costs and maintaining assembly efficiency, with visible recessed portions indicating lead removal for easy inspection.
Implementation Method 1
The masking layer is selectively removed, e.g., via laser ablation, from one or more of the electrically conductive leads
Implementation Method 2
Etching is applied to the second surface of the substrate so that the electrically conductive formations such as leads left uncovered by the masking layer are removed
Data Source
Figure 1~3
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Figure 7A~8
AI summary
One or more semiconductor chips are arranged (102) on a first surface of a substrate comprising electrically conductive formations such as an array of electrically conductive leads covered by a masking layer at a second surface opposite the first surface. The semiconductor chip or chips are coupled to electrically conductive leads in the array and an insulating encapsulation is molded on the semiconductor chip or chips arranged on the first surface of the substrate. The masking layer is selectively removed (110), e.g., via laser ablation, from one or more of the electrically conductive formations that are thus left uncovered by the masking layer. Etching (112) is applied to the second surface of the substrate so that the leads left uncovered by the masking layer are removed, thus increasing the creepage distance between those conductive formations that are left in place.