Asymmetric Lead Frame Design for Power Module Insulation Clearance
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Solution Overview
Problem
In transfer-mold type intelligent power modules, the increase in width due to tie bar cutting residue and overhanging during lead forming operations reduces the insulation clearance distance between electrode terminals, compromising the structural integrity and insulation effectiveness.
Innovation Solution
The introduction of a lead frame design where tie bar cutting residue is either absent or positioned to avoid overlap with the lead forming overhang, ensuring that the connection points for the tie bar on the electrode terminals are distinct on each side surface, thereby maintaining the insulation clearance distance while maintaining the strength of the bent portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the tie bar is thickened to maintain strength of the bent portion, then the strength of the bent portion is improved, but the width of the tie bar connection part increases causing reduction in insulation clearance distance
Solution Approach 1:
The electrode terminal is divided into multiple sections with different thicknesses. The tie bar connection part maintains original thickness rather than being thickened, while the bent portion has sufficient thickness for strength. This segmentation allows the insulation clearance distance to be maintained while still providing adequate strength at the bent portion.
2Ease of operation
If the lead forming operation is applied to ensure attachment to control board, then the ease of operation is improved, but the overhanging causes reduction in insulation clearance distance
Solution Approach 1:
The positions of tie bar connection parts are predetermined and designed in advance to avoid the bending area. The lead frame is designed with specific geometry where tie bars connect at locations that will not overlap with the overhanging portion after lead forming, thus preventing insulation clearance issues before the forming operation occurs.
3Ease of manufacture
If the tie bar cutting residue is present on both side surfaces, then the manufacturing process is simplified, but the distance between electrode terminals is reduced failing to ensure insulation clearance
Solution Approach 1:
The lead frame design creates an asymmetric arrangement where tie bars connect to different side surfaces at different positions. This asymmetry ensures that cutting residue from one tie bar does not overlap with the bending area or adjacent electrode terminals, maintaining insulation clearance while allowing standard cutting processes to be used.
Data Source
AI summary
A transfer-mold type power module includes a plurality of electrode terminals that is arranged so as to protrude in the same direction from a target side surface of a package. A tie bar cutting residue protruding from a first side surface of each of the electrode terminals and a tie bar cutting residue protruding from a second side surface of each of the electrode terminals are different in position in a length direction of each of the electrode terminals. Each of the electrode terminals has a shape bent at a position including tie bar cutting residue closer to the package, with a width direction of each of the electrode terminals as an axis.