Hybrid Ribbon Bonding for Power Packages With Weak Leadframes
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Solution Overview
Problem
Existing methods for electrical coupling in power integrated circuit semiconductor devices, such as power QFN packages, face challenges with clips and ribbons, including precise placement issues, mechanical stress, and cost inefficiencies, particularly when ultrasonic welding is applied to leadframes that are not strong enough.
Innovation Solution
A hybrid ribbon bonding technique is employed, using standard ultrasonic bonding at the die side and conductive tape, glue, or solder as an interface material at the lead side to reduce mechanical stress on the substrate, thereby maintaining the advantages of ribbons without damaging the leadframe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ultrasonic welding is used to bond ribbons to leadframe, then electrical coupling and current transfer are improved, but the leadframe may be damaged due to mechanical stress
Solution Approach 1:
The bonding process is segmented into two distinct stages: first bonding the ribbon to the die, then bonding to the leadframe. This segmentation allows the leadframe bonding to occur under controlled conditions with reduced stress, preventing damage while maintaining electrical coupling reliability.
Solution Approach 2:
The ribbon is preliminarily bonded to the die before being bonded to the leadframe. This preliminary action stabilizes the ribbon and positions it correctly, enabling the subsequent leadframe bonding to proceed with minimal mechanical stress and reduced risk of leadframe damage.
2Strength
If clips are used instead of ribbons to avoid ultrasonic stress, then leadframe damage is prevented, but clip placement precision and stability deteriorate
Solution Approach 1:
The die serves as an intermediary element between the ribbon and leadframe. By bonding the ribbon to the die first, the system achieves stable positioning and precise alignment without requiring precise clip placement on the leadframe, thus maintaining manufacturing precision while preventing leadframe damage.
3Power
If multiple pads and channels are provided in small packages, then current transfer capability is improved, but recess dimensions become small leading to manufacturing difficulties
Solution Approach 1:
The ribbon bonding process is self-aligning through the preliminary bonding to the die, which automatically positions the ribbon correctly without requiring precisely manufactured recesses in the leadframe. This self-service positioning mechanism enables multiple channels in small packages without complicating the manufacturing process.
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 ensures accurate alignment and cost-effectiveness by minimizing mechanical stress on the substrate, allowing for more design flexibility and reducing manufacturing defects and costs.
Implementation Method 1
welding the ribbon at die side (sometimes referred to as 'first' bond) using standard ultrasonic bonding technology
Data Source
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AI summary
One or more integrated circuit semiconductor dice (14) are arranged on a substrate (12) having electrically conductive leads (12B). Electrical coupling of the semiconductor die or dice (14) is provided via electrically conductive ribbons (18) having a first end portion (181) electrically coupled to a semiconductor die (14) and a second end portion (182) electrically coupled to a lead (12B), respectively. The first end portion (181) of the electrically conductive ribbon (18) is ultrasonically coupled (bonded) to the semiconductor die (14), and the second end portion (182) of the electrically conductive ribbon (18) is coupled to the lead (12B) via electrically conductive material, such as film or tape (200) or glue/solder paste (200A, 200B) added at the second end portion 182 of the electrically conductive ribbon (18).