Leadframe Package Side Solder Ball Contact for Joint Strength
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Solution Overview
Problem
Surface mount leadframe packages lack solder wettable material on the sidewall, leading to weakened solder joints and reduced reliability due to different coefficients of thermal expansion between the package and the PCB, and existing solutions like post-manufacturing plating are inefficient and lack automated inspection capabilities.
Innovation Solution
Incorporating solder balls on the sidewall of the leadframe package that extend into the encapsulant, allowing solder to form integral connections with the leadframe and substrate, increasing the solder contact area and reducing thermal resistance, which can be achieved through pre-plating of the leadframe, forming recesses for solder balls, and ensuring compatibility with the encapsulant material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If surface mount technology is used to reduce package size, then package size is reduced, but solder joint strength is weakened due to lack of sidewall solder contact
Solution Approach 1:
The invention transitions from traditional bottom-only solder contact (2D planar contact) to include sidewall solder contact (3D multi-dimensional contact). By placing solder balls on the sidewalls of the leadframe package, the solder joint contact area is extended from a single plane to multiple surfaces, thereby increasing overall joint strength while maintaining the compact package size enabled by surface mount technology.
Solution Approach 2:
The solder joint connection is divided into multiple segments: bottom solder contact and sidewall solder contact. This segmentation allows the total solder joint strength to be distributed across multiple contact points, with each solder ball on the sidewall contributing independently to the overall joint strength, compensating for the reduced contact area due to smaller package size.
2Strength
If post-manufacturing plating is added to provide sidewall solder contact, then solder joint strength is improved, but manufacturing complexity and cost increase
Solution Approach 1:
Solder balls are placed on the sidewalls of the leadframe package during the manufacturing process, before the package is completed and shipped. This preliminary placement of solder contact material eliminates the need for post-manufacturing plating operations, as the solder balls are already positioned to provide the necessary sidewall contact when the package is assembled to the circuit board.
Solution Approach 2:
Solder balls serve as intermediary elements between the leadframe package sidewalls and the circuit board solder joints. Instead of directly plating the sidewalls with solder material, the invention uses discrete solder balls as mediators that provide the necessary solder contact surface, simplifying the manufacturing process while achieving the same functional result.
3Strength
If post-manufacturing plating is used to add solder material, then sidewall solder contact is provided, but automated inspection capability is lost
Solution Approach 1:
The solder balls placed on the sidewalls have distinct visual characteristics (spherical shape, metallic reflectivity, specific size) that differ from the surrounding package components. These visual properties enable automated optical inspection systems to easily detect and verify the presence, position, and integrity of the solder balls on the sidewalls, maintaining automated inspection capability that would be lost with conventional plating methods.
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 enhances the strength and reliability of solder joints, reduces the number of pins required, and enables automated inspection, leading to improved package reliability and increased signal/data pins without the need for additional plating steps.
Implementation Method 1
When the package is attached to a substrate, solder flows between the leadframe and the substrate and forms a connection with the solder ball to create an integral solder joint
Implementation Method 2
flowing the solder ball during the original placement in order to form a bond between the metal plating layer on the leadframe and the solder ball
Data Source
AI summary
The present disclosure is directed to a leadframe package having a side solder ball contact and methods of manufacturing the same. A plurality of solder balls are coupled to recesses in a leadframe before encapsulation and singulation. After singulation, a portion of each solder ball is exposed on sidewalls of the package. This ensures that the sidewalls of the leads are solder wettable, which allows for the formation of stronger joints when the package is coupled to a substrate. This increased adhesion reduces resistance at the joints and also mitigates the effects of expansion of the components in the package such that delamination is less likely to occur. As a result, packages with a side solder ball contact have increased life cycle expectancies.