Lead Frame Manufacturing for QFN Packages
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Solution Overview
Problem
Current multi-row quad flat non-leaded (QFN) packages face challenges such as reduced die size due to additional rows of leads, increased manufacturing costs, and the inability to perform electrolytic solder plating on isolated leads.
Innovation Solution
A method involving an electrically conductive layer with holes filled with non-conductive material, etched to create a network of leads, die pad, bus lines, dam bars, and tie lines, with a solder mask covering inner rows and exposing outer rows for electrolytic solder plating, allowing for increased lead rows without reducing die size and enabling electrolytic processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If additional rows of leads are added to increase I/Os, then the number of input/outputs increases, but the die pad area must be reduced to accommodate the additional leads
Solution Approach 1:
The patent transitions from a planar lead arrangement to a three-dimensional structure by forming leads that extend through the mold compound and connect to an internal electrically conductive layer. This vertical dimension allows additional I/Os without consuming horizontal die pad area, as leads are routed through the package depth rather than expanding the perimeter.
Solution Approach 2:
The patent embeds an electrically conductive layer within the mold compound, creating a nested structure where the conductive layer is contained inside the package body. This internal layer provides additional lead pathways without occupying external space, effectively nesting functional elements within the package volume to increase I/O capacity while maintaining compact dimensions.
2Area of stationary object
If the package size is increased to maintain die size and accommodate additional rows of leads, then the die size can be maintained, but manufacturing costs increase and circuit design is affected
Solution Approach 1:
Instead of increasing package footprint to maintain die size, the patent utilizes the vertical dimension by forming leads that extend through the mold compound to an internal conductive layer. This three-dimensional lead routing allows the package to maintain compact dimensions while preserving die size, avoiding the cost increases associated with larger packages.
3Reliability
If leads are isolated from one another in the assembled package, then individual lead connectivity is achieved, but electrolytic solder plating cannot be performed on the exposed leads
Solution Approach 1:
The patent introduces an electrically conductive layer as an intermediary within the mold compound that provides continuous electrical connectivity between all isolated leads. This internal conductive network acts as a mediator, allowing electrolytic solder plating to be performed on the external leads through the conductive pathway provided by the internal layer, even though the leads are physically isolated from each other in the assembled package.
Data Source
AI summary
A method of manufacturing a lead frame includes providing an electrically conductive layer having a plurality of holes at a top surface. The plurality of holes form a structure of leads and a die pad on the electrically conductive layer. The plurality of holes are filled with a non-conductive material. Next; an electrically conductive foil is attached on the top surface of the electrically conductive layer and the non-conductive epoxy material. The, the electrically conductive foil is etched to create a network of leads, die pad, bus lines, dam bars and tie lines, wherein the bus lines connect the leads to the dam bar, the dam bar is connected to the tie line and the tie line is connected to the die pad.