Leadframe Recesses Contain Adhesive Creep for Thinner Dies
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Solution Overview
Problem
Adhesive creep in semiconductor packages causes electrical or thermal coupling issues and prevents successful wire bonding, especially with thin semiconductor dice, as current adhesives can only be used effectively with dice thicker than 150 micrometers to prevent adhesive from creeping up the side surfaces.
Innovation Solution
A leadframe design with etched recesses acts as overflow reservoirs to collect excess adhesive, preventing it from reaching the perimeter of the die and climbing up the side surfaces, and encapsulant anchors reinforce the connection between the encapsulant and the leadframe, enhancing mechanical strength and moisture barrier properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adhesive is used to attach die to leadframe, then electrical and thermal characteristics are improved, but adhesive creep causes harmful coupling between adhesive and contacts
Solution Approach 1:
The recess acts as an intermediary structure between the adhesive and the die side surface. It provides a designated area for adhesive overflow, preventing direct contact between the adhesive and the die side surface, thereby eliminating the harmful coupling effect while maintaining the beneficial electrical and thermal characteristics of the adhesive.
Solution Approach 2:
The harmful function of adhesive (creep causing coupling) is separated from its useful function (providing electrical and thermal characteristics). By providing a recess, the adhesive's overflow is directed away from the die side surface, extracting the harmful creeping action from the bonding interface while preserving the adhesive's primary bonding, electrical, and thermal functions.
2Length of moving object
If die thickness is reduced to improve miniaturization, then device size is reduced, but adhesive creep more easily reaches top surface contacts
Solution Approach 1:
The recess serves as a mediator that intercepts adhesive overflow before it can reach the die side surface. This allows the use of thinner dies without increasing the risk of adhesive creep contacting the top surface contacts, as the recess provides a physical barrier and overflow reservoir.
Solution Approach 2:
The solution moves from a one-dimensional approach (relying on die thickness to prevent creep) to a two-dimensional approach (using the recess structure to contain adhesive). By adding the recess dimension, the system can accommodate thinner dies while maintaining protection against adhesive creep.
3Reliability
If adhesive amount is increased to ensure proper bonding, then bonding reliability is improved, but excess adhesive flows to die perimeter and creeps up side surface
Solution Approach 1:
The excess adhesive, which would normally be a harmful overflow causing creep, is converted into a beneficial feature by providing a designated home for it in the recess. The adhesive's natural tendency to flow and spread is harnessed to fill the recess, preventing harmful creep while maintaining proper bonding.
Solution Approach 2:
The recess acts as an intermediary reservoir that accepts excess adhesive. This allows increased adhesive application for bonding reliability while preventing the harmful effects of overflow, as the recess intermediates between the excess adhesive and the die side surface.
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 leadframe design effectively prevents adhesive creep, allowing for the use of thinner semiconductor dice by containing excess adhesive within recesses and reinforcing the encapsulant connection, thereby improving manufacturing tolerances and preventing electrical or thermal coupling issues.
Implementation Method 1
a layer of adhesive 114 on the top surface 104
Implementation Method 2
the entire assembly is covered with an encapsulant 406
Data Source
AI summary
The present disclosure is directed to a leadframe having a recess in a body of the leadframe to collect glue overflowing from the manufacturing process of coupling a semiconductor die to the leadframe. The recess extends beneath an edge of the semiconductor die so that any tendency of the glue to adhere to the semiconductor die is counteracted by a tendency of the glue to adhere to a wall of the recess and at least partially fill the volume of the recess. In addition, the recess for collecting adhesive may also form a mold lock on an edge of the leadframe, the mold lock providing a more durable connection between the leadframe and an encapsulant during physical and temperature stresses.