IC Package Lead Tabs for Oxidation-Resistant Solder Joints
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Solution Overview
Problem
During the singulation process of integrated circuit packaging, the exposure of base metal on lead frame strips to air leads to oxidation, preventing solder from forming reliable joints with the oxidized metal, resulting in weak solder connections and potential delamination.
Innovation Solution
The introduction of solder joint reinforcement tabs with a solderable metal layer on specific sides and portions of the tabs, which extend from the periphery of the IC package, providing an increased wettable area for solder to form strong and reliable joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lead frame strips are cut through during singulation, then individual packages are separated, but base metal is exposed and oxidizes preventing reliable solder joints
Solution Approach 1:
A solderable metal layer is applied to the lead frame strip before the singulation process. This preliminary plating ensures that when the strip is cut during singulation, the exposed surfaces already have a solderable coating, preventing oxidation issues and ensuring reliable solder joints without requiring additional post-singulation plating steps.
Solution Approach 2:
A solderable metal layer acts as an intermediary between the base metal and the solder joint. This intermediate layer prevents direct exposure of the base metal to oxidizing environments during singulation and provides a surface that is both oxidation-resistant and solderable, resolving the contradiction between efficient singulation and reliable soldering.
2Ease of manufacture
If base metal is exposed during singulation, then cutting is completed, but oxidation prevents solder from wetting the metal surface
Solution Approach 1:
The base metal surfaces are pre-plated with a solderable metal layer before singulation. This preliminary protective coating prevents oxidation during the cutting process, allowing simple singulation operations without requiring complex oxidation prevention measures during manufacturing.
Solution Approach 2:
The solderable metal layer creates an inert-protected environment for the base metal during singulation. By replacing the reactive base metal surface with a stable, oxidation-resistant metal layer, the harmful oxidative environment during cutting is effectively neutralized without requiring actual inert gas atmospheres.
3Reliability
If solderable metal layer is applied to lead frame strip, then oxidation is prevented, but additional manufacturing steps are required
Solution Approach 1:
The plating process is merged with the existing lead frame manufacturing process. By applying the solderable metal layer during standard lead frame production rather than as a separate post-processing step, the additional manufacturing complexity is minimized while ensuring reliable solder joints are achieved.
Solution Approach 2:
The solderable metal layer serves multiple functions simultaneously: it prevents oxidation of the base metal during storage and processing, provides a solderable surface for reliable joints, and eliminates the need for additional post-singulation plating steps. This multi-functionality reduces overall process complexity despite the initial plating step.
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
The use of solder joint reinforcement tabs enhances the formation of robust solder joints between the integrated circuit package and the printed circuit board, reducing the likelihood of delamination and field failures while maintaining minimal additional costs.
Implementation Method 1
The layer of solderable metal is intended to prevent oxidation of the lead frame base metal, which occurs when the base metal is exposed to air.
Implementation Method 2
Solder is not able to properly wet any oxidation layer that forms, and the solder cannot form a reliable solder joint to the oxidized base metal.
Data Source
AI summary
In a described example, an integrated circuit (IC) package includes an IC die disposed on a die attach pad; a plurality of leads electrically connected to terminals on the IC die, the leads including a base metal; and molding compound material encapsulating portions of the IC die, the die attach pads, and the plurality of leads; the plurality of leads having a solder joint reinforcement tab. The solder joint reinforcement tabs include a first side, a second side opposite to the first side, a third side, a fourth side opposite to and in parallel to the third side, a fifth side forming an end portion of the solder joint reinforcement tab, the solder joint reinforcement tabs including a solderable metal layer on the second, third and fourth sides and on portions of the fifth side.