Preformed Lead Frame with Etched Grooves for Reliable Connections
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Solution Overview
Problem
Conventional flat no-lead packages face challenges in providing reliable electrical and mechanical connections during reflow soldering due to insufficient wettable flanks, and existing solutions involve complex and costly manufacturing processes.
Innovation Solution
A preformed lead frame with intersecting cutting paths and a molding layer that includes metallic connecting portions and etched grooves, which increases the contact area with solder material, enhancing electrical and mechanical connections and simplifying the dicing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a conventional flat no-lead package is used, then the package size is reduced, but the wettable flanks are insufficient for reliable connections
Solution Approach 1:
The lead frame is pre-formed with connecting portions and etched grooves before encapsulation. The connecting portions are designed to extend upwardly from the bottom surface of the molding layer, creating increased wettable flanks that will contact solder material during reflow soldering. This preliminary structuring ensures reliable connections are built into the design before final packaging.
Solution Approach 2:
The connecting portions extend in the vertical dimension (upwardly from the bottom surface of the molding layer), adding a third-dimensional feature to the otherwise flat package structure. This vertical extension creates additional wettable surface area without increasing the horizontal package footprint, thus maintaining small package size while improving connection reliability.
2Reliability
If step cuts are formed to increase wettable flanks, then connection reliability is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The connecting portions and etched grooves are incorporated into the lead frame design before encapsulation in the molding layer. This preliminary formation allows the wettable flanks to be created during the molding process itself, rather than requiring subsequent complex dicing operations to form step cuts. The connecting portions are formed as integral parts of the lead frame structure, simplifying the overall manufacturing process.
Solution Approach 2:
The molding layer itself serves the dual function of encapsulating the lead frame and IC chip while simultaneously forming the connecting portions that provide wettable flanks. The molding process automatically creates the upwardly extending connecting portions with etched grooves, eliminating the need for separate operations to create these connection-enhancing features.
3Area of stationary object
If multiple cutting steps are performed after encapsulation, then connection area is increased, but manufacturing time and cost increase
Solution Approach 1:
The connecting portions are pre-formed during the lead frame fabrication and molding processes, before the final encapsulation is complete. The etched grooves are created in the molding layer during molding, not after. This preliminary formation of the connection structure eliminates the need for time-consuming post-encapsulation dicing operations to create step cuts or expose additional wettable surfaces.
Solution Approach 2:
The functions of encapsulation and connection structure formation are merged into a single molding process. The molding layer simultaneously protects the IC chip and lead frame while creating the upwardly extending connecting portions with etched grooves that provide wettable flanks. This consolidation of functions reduces the total number of manufacturing steps and associated time.
Data Source
AI summary
A preformed lead frame includes a plurality of lead frame units and intersecting cutting paths extending between two adjacent rows of said lead frame units, and a molding layer. Each of the lead frame units includes a die pad, and a plurality of spaced-apart leads. Each of the cutting paths has a plurality of metallic connecting portions and etched grooves. The molding layer embeds the lead frame units and the connecting portions. Each of the etched grooves is indented from the top surface of the molding layer. A top open end of each of the etched grooves includes two opposite curved edges respectively meeting an adjacent one of the leads of one of the lead frame units and an adjacent one of the leads of the other one of the lead frame units.