QFN Leadless Package with Fishtail Tie-Bar for High Pad Count
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Solution Overview
Problem
The demand for higher input/output terminal pad count in integrated circuit packaging is not met by conventional leadframe designs, which are limited by lead spacing and tie-bar location, necessitating a new approach to increase terminal pads while reducing package size and cost.
Innovation Solution
The integrated circuit leadless package system employs a QFN leadframe with fishtail tie-bars, additional outer contact pads, and staggered inner contact pads, allowing for increased terminal pads without the need for lead frames, and uses bond wires to connect the IC to these pads, with a molding compound for protection and heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional leadframe designs are used, then manufacturing process is simple, but terminal pad count is limited
Solution Approach 1:
The patent removes the leadframe structure entirely from the package design, extracting only the essential function of electrical connection through exposed pad contacts. This eliminates the constraint of lead spacing and tie-bar location that limited terminal pad count in conventional designs, allowing pads to be arranged in any configuration on the exposed surface.
Solution Approach 2:
The patent transitions from a two-dimensional leadframe layout to a three-dimensional exposed pad structure where terminals can be arranged on the bottom surface and potentially on multiple levels. This dimensional change allows for increased terminal density without increasing the planar footprint of the package.
2Quantity of substance
If lead spacing is reduced to increase terminal pads, then terminal pad count increases, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses a sacrificial mandrel structure that is removed after bonding. This disposable mandrel allows for precise pad positioning to be achieved during manufacturing, then the mandrel is discarded, leaving the final package with no precision-critical components requiring tight tolerances.
3Volume of moving object
If package size is reduced, then device miniaturization is achieved, but terminal pad count increases difficultly
Solution Approach 1:
The patent nests the bond wires within the molding compound, and nests the exposed pads within the package footprint by utilizing the bottom surface area. This nesting approach allows maximum utilization of the package volume and surface area to accommodate more terminals without increasing the external dimensions.
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
This design enables a higher number of contact pads in a smaller package size, extending the useful life of assembly machines, reducing costs, and enhancing performance, while maintaining compatibility with conventional manufacturing processes.
Implementation Method 1
Wire-bonding pads on the die are then connected to selected ones of the inner ends of the leads by fine, conductive bond wires to convey power, ground, and signals between the die and the leads.
Implementation Method 2
A protective body of an epoxy resin is molded over the assembly to enclose and seal the die, the inner ends of the leads, and the wire bonds against harmful environmental elements.
Implementation Method 3
the die pad is 'down-set' relative to the plane of the leads such that its lower surface is exposed through the lower surface of the body for enhanced dissipation of heat from the die
Data Source
AI summary
An integrated circuit leadless package system is presented comprising forming a QFN leadframe comprises providing a die pad, forming a fishtail tie-bar on the die pad, forming a row of an outer contact pad around the die pad, forming an additional outer contact pad around the fishtail tie-bar, and forming an inner contact pad in a staggered position from the outer contact pad, mounting an integrated circuit on the die pad of the QFN leadframe, and attaching a bond wire from the integrated circuit to the additional outer contact pad.