QFN Lead Frame Indents Mitigate Saw Burrs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The sawing process in manufacturing quad flat no-lead (QFN) packages can lead to material deformation, burr formation, and reduced lead spacing, causing voltage withstand issues and potential short circuits, which existing solutions like hybrid saw blades or low-temperature cutting water increase production costs and complexity.
Innovation Solution
A lead frame design with rhomboid-shaped leads featuring first and second indents on their lateral sides, which facilitates reduced lead smearing and burr generation during sawing, maintaining proper lead spacing without additional cost or complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sawing is used to separate packaged devices, then production cost is low, but lead deformation and burr formation occur causing reduced lead spacing and potential short circuits
Solution Approach 1:
The lead frame is pre-formed with indented regions at the lateral sides of leads before the sawing process. These indents create a geometric feature that causes the saw blade to depart from the lead rather than continue cutting along it, preventing burr formation and lead smearing before they can occur during separation
Solution Approach 2:
The indented regions introduce a curved or non-linear geometric feature into the otherwise straight lead structure. This curvature change at the lateral sides modifies the interaction between the saw blade and lead, causing the blade to follow the indent contour and depart cleanly without generating harmful burrs or smearing
2Reliability
If hybrid saw blades are used to reduce heat and burr generation, then lead deformation is reduced, but production tooling costs increase
Solution Approach 1:
The lead frame structure itself provides the solution to its own sawing problems through the pre-formed indented regions. The indents create a self-guiding feature that directs the saw blade path and prevents harmful interactions, eliminating the need for expensive hybrid saw blades or additional cooling systems
Solution Approach 2:
The harmful function of the saw blade (causing lead deformation and burr generation) is extracted and redirected by the indented regions. The indents cause the saw blade to follow a modified path that separates it from direct contact with the lead body, effectively removing the harmful cutting action from the lead while maintaining the necessary separation function
3Manufacturing precision
If nozzles with low temperature cutting water are used to cool the saw blade, then burr generation is reduced, but system complexity and cost increase
Solution Approach 1:
The lead frame structure itself provides the solution to thermal management during sawing through its indented regions. The indents create a geometric path that naturally limits heat generation by reducing direct saw-lead contact, eliminating the need for external cooling systems with nozzles and water delivery mechanisms
4Reliability
If copper lead frame thickness is reduced to minimize heat absorption, then heat-related deformation is reduced, but electrical and structural performance deteriorates
Solution Approach 1:
The indented regions are pre-formed in the lead frame structure to create a geometric configuration that limits saw blade contact with the lead. This preliminary structural modification allows the use of standard thickness copper leads that maintain both electrical/structural performance and heat resistance during the sawing process
Data Source
AI summary
A lead frame includes a metal structure having opposite first and second sides and prospective device portions having leads with first and second lateral sides extending from a tie bar toward a die attach pad. One or more of the leads includes a first indent in the first lateral side that extends to the first side of the metal structure, and a second indent that extends to the second side of the metal to reduce saw blade loading and mitigate saw burr and lead smear during package singulation. A packaged electronic device includes a package structure, a semiconductor die enclosed by the package structure, and leads having a first side, a second side, and first and second lateral sides, where the leads include a first indent in the first lateral side that extends to the first side, and a second indent that extends to the second side of the lead.