Lead Frame Raised Portion Prevents Saw Blade Adhesion
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Solution Overview
Problem
In QFN package semiconductor device manufacturing, metal burrs left on connecting bars can cause short circuits, and leaving non-half-etched portions to prevent this reduces the stiffness of the connecting bars, while external plating processes can dull saw blades due to adhering solder-plating layers.
Innovation Solution
A lead frame design with raised portions on the connecting bars, positioned between the lead portions and the connecting bar surfaces, prevents solder-plating layer adhesion to saw blades and maintains the stiffness of the connecting bars by ensuring the raised portions are not exposed during encapsulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If half-etched recessed portions are provided to the connecting bars to prevent metal burrs, then metal burrs are prevented from remaining on the connecting bars, but the stiffness of the connecting bars is reduced
Solution Approach 1:
The connecting bar is designed with a raised portion that creates a localized structural feature. This raised portion is positioned such that it prevents metal burrs from remaining on the connecting bar surface while maintaining the overall stiffness of the connecting bar. The local modification does not compromise the global structural integrity.
2Reliability
If non-half-etched portions are left on the back surface of the connecting bars, then metal burrs are prevented from remaining, but solder-plating layers adhere to saw blades during the sawing process
Solution Approach 1:
The raised portion creates a localized topography on the connecting bar that prevents solder-plating layer adhesion to the saw blade during sawing. The specific geometry of the raised portion ensures that the solder-plating layer does not come into contact with the saw blade edge, eliminating the harmful adhesion effect while maintaining the benefit of preventing metal burrs.
Solution Approach 2:
Instead of leaving the connecting bar surface flat or recessed (conventional approach), the invention inverts the approach by creating a raised portion. This inverted geometry achieves the desired effect of preventing both metal burrs and solder-plating layer adhesion, as the raised portion protrudes in the opposite direction to conventional recessed designs.
3Object-generated harmful factors
If the raised portion tip is positioned between the lead portion first surface and connecting bar first surface, then solder-plating layer adhesion to saw blades is prevented, but the structural complexity increases
Solution Approach 1:
The raised portion is designed as a simple localized feature with specific dimensional constraints (tip position between two surfaces). This local modification is straightforward to implement in the manufacturing process and does not require complex overall restructuring of the connecting bar, thus minimizing the increase in structural complexity while achieving the desired prevention of solder-plating layer adhesion.
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
The raised portion design prevents solder-plating layer adhesion to saw blades during the sawing process, maintaining the stiffness of the connecting bars and ensuring efficient semiconductor device separation without tool dulling.
Implementation Method 1
The process of manufacturing such QFN package semiconductor devices starts with etching on a metal plate to produce a lead frame.
Implementation Method 2
a semiconductor element that is mounted on a mount surface of a lead frame and encapsulated with encapsulation resin
Implementation Method 3
the next process of manufacturing the QFN package semiconductor devices is sawing, in which the encapsulation resin and the connecting bars are cut off with a saw blade
Implementation Method 4
In the external plating process, an external plating layer such as a solder-plating layer is deposited on the portions exposed from the encapsulation resin on the back surface of the lead frame.
Data Source
AI summary
A lead frame includes a lead portion having a first surface and a second surface, a connecting bar that has a first surface and a second surface and to which the lead portion is connected, and a raised portion provided on the first surface of the connecting bar. The first surface of the connecting bar is positioned between the first and the second surfaces of the lead portion. The tip of the raised portion is positioned between the first surface of the lead portion and the first surface of the connecting bar.