Leadframe Connecting Bar Ablation for Clean Die Singulation
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Solution Overview
Problem
The formation of filaments and flakes during the singulation step in semiconductor device manufacturing due to the accumulation of metallic material on connecting bars causes short circuits between neighboring leads, leading to device failure and rejection.
Innovation Solution
The method involves removing the metallic material accumulated on the connecting bars via laser ablation before the singulation step, specifically targeting the tie bars and extending beyond the width of the connecting bars to prevent filament formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If large connecting bars are used during plating to facilitate processing, then plating is improved, but filament formation during singulation causes short circuits
Solution Approach 1:
The patent applies preliminary action by performing laser ablation of the metallic layer on connecting bars before the singulation step. This removes excess metal accumulated during plating in advance, preventing filament formation during subsequent blade cutting. The metallic layer is selectively removed from connecting bars while preserving it on leadframe bottom surfaces, ensuring clean separation without short circuits.
2Reliability
If metallic layer is plated on connecting bars during plating step, then solderability is improved, but excess metal accumulation causes filament formation
Solution Approach 1:
The patent applies local quality by selectively removing the metallic layer only from specific locations - the connecting bars - while preserving it on the leadframe bottom surfaces. This localized treatment maintains solderability where needed (on leadframe bottoms) while eliminating the harmful effect of excess metal on connecting bars that causes filament formation during singulation.
Solution Approach 2:
The patent extracts the harmful excess metallic material from the connecting bars using laser ablation before singulation. This removal action separates the useful metallic layer (needed for solderability on leadframe bottoms) from the harmful accumulation (on connecting bars that causes filaments), allowing the useful function to be preserved while eliminating the harmful effect.
3Productivity
If blade singulation is performed on plated connecting bars, then device separation is achieved, but metal flakes bridge neighboring leads causing short circuits
Solution Approach 1:
The patent performs preliminary laser ablation to remove the metallic layer from connecting bars before the blade singulation step. This preliminary action prevents metal flakes from being generated during blade cutting, ensuring clean separation of neighboring leads without bridging or short circuits, while maintaining efficient productivity.
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 effectively reduces the risk of short circuits by eliminating the metallic layer at critical points, ensuring the integrity of the singulated devices without compromising solderability.
Implementation Method 1
metallic material accumulated on the back/bottom surface of the connecting bars is removed via laser ablation
Data Source
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AI summary
A plurality of semiconductor chips or dice are arranged onto a first surface of a common electrically conductive substrate (12). The common substrate (12) has a second surface opposite the first surface and comprises adjacent substrate portions (120) having mutually facing sides with elongate sacrificial connecting bars (CB) extending between adjacent mutually facing sides. A solderable metallic layer (e.g., tin) is grown on the second surface of the common electrically conductive substrate (12) so that the solderable metallic layer extends over the connecting bars (CB). The solderable metallic layer is removed (e.g. via laser ablation) from at least part of the length the sacrificial connecting bars (CB). The common electrically conductive substrate (12) with the plurality of semiconductor dice arranged onto the first surface is cut to provide singulated individual semiconductor devices. Cutting is along the length of the elongate sacrificial connecting bars (CB) having the solderable metallic layer at least partly removed. In that way, undesired formation of electrically conductive filaments or flakes bridging parts of the substrate intended to be mutually isolated is countered.