Lead Frame Constricted Ends Prevent Wire Sweep Short Circuits
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Solution Overview
Problem
In semiconductor devices with multiple pins and leads of small pitch, wire sweep during resin molding can cause short circuits due to the deformation of wires and the inability to sharply cut leads with insulating tape, leading to installation and bonding accuracy issues.
Innovation Solution
A lead frame design with leads having constricted sides forming an angle of 75° to 105° relative to the resin flow direction, where the constricted side has a smaller width than the lead thickness, and frame insulating tape is used between the radiator plate and lead ends, allowing for precise cutting and bonding to prevent wire sweep-induced short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of pins is increased and the pitch of leads is reduced to achieve higher density, then the functionality and density of the semiconductor device are improved, but the leads are deformed and wire sweep causes short circuits
Solution Approach 1:
The patent applies local quality by providing constricted portions at specific locations on the leads (at the ends or near the ends) while maintaining the original lead width in other portions. This localized modification prevents wire sweep-induced short circuits without affecting the overall lead structure and electrical connectivity, thereby resolving the contradiction between increased pin density and manufacturing precision.
Solution Approach 2:
The constricted portions are formed in advance during the lead frame manufacturing process, before the semiconductor chip mounting and wire bonding steps. This preliminary action ensures that when wires are later bonded to the leads, the constricted portions are already in place to prevent wire sweep from causing short circuits, thus maintaining manufacturing precision even with high pin density.
2Stability of the object's composition
If insulating tape is used to fix the leads to prevent deformation, then lead stability is improved, but the ends of leads cannot be sharply cut due to the tape
Solution Approach 1:
The patent segments the lead structure into different portions: fixed portions that are bonded to the insulating tape for stability, and end portions with constricted portions that extend beyond the tape for precise cutting. This segmentation allows the lead ends to be sharply cut even when the leads are fixed with insulating tape, resolving the contradiction between lead stability and cutting precision.
Solution Approach 2:
The constricted portions extend in the direction protruding from the frame in a manner that overlaps the inner frame of the insulating tape, creating a three-dimensional arrangement. This dimensional arrangement allows the lead ends to be precisely cut while the leads remain stabilized by the insulating tape, resolving the contradiction between stability and cutting precision.
3Quantity of substance
If the pitch of leads is reduced to increase pin density, then the functionality is improved, but wire sweep during resin molding causes short circuits between adjacent leads
Solution Approach 1:
The constricted portions are localized at specific positions on the leads where wire bonding occurs, providing targeted protection against wire sweep-induced short circuits. This local modification maintains the small pitch between leads for high density while preventing short circuits through the constricted portions that restrict wire movement.
Solution Approach 2:
The constricted portions transform the potential harm of wire sweep into a beneficial effect by using the constricted geometry to restrict wire movement and prevent short circuits. The constricted portions act as mechanical stops that prevent wires from sweeping across to adjacent leads, thereby converting the wire bonding process from a potential source of short circuits to a reliable connection method even at high pin densities.
Data Source
AI summary
A lead frame is provided which can prevent a short circuit between wires and the ends of adjacent leads, the short circuit being caused by wire sweep during the injection of molding resin, in a configuration where the electrodes of a semiconductor chip and the leads disposed around the semiconductor chip. The lead having sides substantially perpendicular to the direction of a resin flow has an end whose upstream side relative to the resin flow is constricted.