QFN Lead Frame Solder Anchoring Tabs via Sacrificial Material
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
QFN packaging faces issues such as strip handling damage, lead frame instability during bond wire formation, and insufficient solder anchoring during package surface mounting, particularly as lead dimensions decrease.
Innovation Solution
The method involves using a lead frame with a recess and a sacrificial material, such as a thermally decomposable polymer, to create solder anchoring tabs and sidewall recesses, enhancing stiffness and solder anchoring performance, while maintaining compatibility with existing saw-type QFN manufacturing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If lead dimensions are decreased to achieve smaller package size, then package footprint is reduced, but strip handling damage and lead frame instability increase
Solution Approach 1:
The patent applies preliminary action by forming sacrificial material in recesses of the lead frame before mounting the IC. This sacrificial material serves as a temporary structural support that prevents strip handling damage and lead frame instability during bond wire formation. After the bonding process, the sacrificial material is removed to create sidewall recesses, leaving the lead frame structurally sound. This preliminary reinforcement allows the use of smaller lead dimensions while maintaining reliability during critical manufacturing steps.
2Ease of manufacture
If traditional QFN packaging is used without sidewall recesses, then manufacturing is simpler, but solder anchoring during package surface mounting is insufficient
Solution Approach 1:
The patent applies segmentation by dividing the lead frame structure into distinct functional zones: traditional mold anchoring tabs for IC attachment, and new sidewall recesses with solder anchoring tabs for enhanced soldering. The sacrificial material removal process creates these segmented sidewall recesses that provide additional surfaces for solder anchoring. This segmentation allows the package to maintain simple manufacturing processes while significantly improving solder anchoring capability through the added vertical soldering surfaces.
3Reliability
If sacrificial material is added to create sidewall recesses, then solder anchoring is enhanced, but device structure becomes more complex
Solution Approach 1:
The patent uses sacrificial material as an intermediary substance that temporarily occupies the recess space during manufacturing, then is removed to create the final sidewall recess structure. This intermediary approach allows the sidewall recesses to be formed using existing saw-type manufacturing equipment without requiring complex new tooling. The sacrificial material enables the creation of enhanced solder anchoring structures while maintaining compatibility with standard manufacturing processes, thus limiting the increase in device complexity.
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 approach reduces strip handling damage, improves bond wire formation stability, and enhances solder anchoring, resulting in improved board level reliability and a 41% increase in normalized solder life.
Implementation Method 1
forming a sacrificial material in the recess of the lead frame... The sacrificial material may comprise at least one of a thermally decomposable material
Data Source
AI summary
A method is for making a semiconductor device. The method may include providing a lead frame having a recess, forming a sacrificial material in the recess of the lead frame, and mounting an IC on the lead frame. The method may include encapsulating the IC and the lead frame, removing portions of the lead frame to define lead frame contacts for the IC, and removing the sacrificial material to define for each lead frame contact a solder anchoring tab extending outwardly at a lower region and defining a sidewall recess between opposing portions of the solder anchoring tab and the encapsulation material.