Staggered Lead Frame Design for QFN Mounting Reliability
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Solution Overview
Problem
Conventional QFN semiconductor packages with a large number of pins face challenges in maintaining mounting reliability due to increased size, leading to longer bonding wires and higher manufacturing costs, and the strength of half-etched lead portions is insufficient, potentially causing deformation and yield reduction.
Innovation Solution
A lead frame design with alternately staggered external terminals, where the inside and outside regions of the lead portions have thinner rear surfaces compared to the external terminal regions, and the outside region has a convexed portion projecting downward, enhancing the geometrical moment of inertia and preventing deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of pins is increased to meet demand for advanced power supplies and microcomputers, then the functionality and application range are improved, but the package size becomes larger and mounting reliability deteriorates
Solution Approach 1:
The patent transitions from a conventional single-row terminal arrangement to a dual-row staggered arrangement, effectively utilizing two dimensions for terminal placement. This allows increasing the number of pins without proportionally increasing the package size, as terminals are distributed across two rows with alternating inside/outside positions, improving space utilization and maintaining compact dimensions while enhancing functionality.
Solution Approach 2:
The patent employs asymmetric design in the lead portion structure by creating different thickness regions (first thickness region with greater thickness, second thickness region with smaller thickness) and positioning external terminals alternately on inside and outside. This asymmetric configuration optimizes structural strength distribution and enables compact packaging while maintaining mounting reliability.
2Quantity of substance
If the package size is increased to accommodate more pins, then the number of terminals is improved, but the bonding wire length increases and manufacturing cost rises
Solution Approach 1:
By arranging terminals in a dual-row staggered configuration rather than a single extended row, the patent reduces the linear distance between corresponding internal and external terminals. This dimensional reorganization allows more terminals to be packed into a compact area, thereby reducing bonding wire length and material consumption while maintaining the required terminal quantity.
3Quantity of substance
If the width of lead portions is reduced to accommodate more pins, then the number of terminals is improved, but the strength of lead portions becomes insufficient and deformation occurs
Solution Approach 1:
The patent applies local quality by creating distinct thickness regions within the lead portions - a first thickness region with greater thickness for enhanced strength and a second thickness region with smaller thickness for compactness. This localized variation in structural properties allows the lead portions to maintain adequate strength despite reduced overall width, preventing deformation while accommodating more terminals.
Solution Approach 2:
The asymmetric thickness distribution in lead portions, with alternating inside and outside terminal positions, creates optimized structural support where needed. The greater thickness in the first thickness region provides reinforcement at critical locations, enabling narrower lead portions to maintain sufficient strength for the increased number of terminals.
Data Source
AI summary
A lead frame includes a die pad and a plurality of lead portions each including an internal terminal and an external terminal. The external terminals of the plurality of lead portions are arranged in an alternately staggered form such that the respective external terminals of a pair of lead portions adjacent to each other are alternatively located on an inside or an outside. A lead portion has an inside region located on the inside of a first external terminal, an outside region located on the outside of the first external terminal, and an external terminal region having the first external terminal. The inside region and the outside region are each formed thin by means of half etching. A maximum thickness of the outside region is larger than a maximum thickness of the inside region.