Deflecting Tie Bar Lead Frame for IC Package
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Solution Overview
Problem
The compressive force applied during the encapsulation phase of packaged IC device assembly can cause physical damage to the IC die due to the molding compound covering the heatsink, inhibiting heat dissipation and potentially cracking the die.
Innovation Solution
A lead frame design with deflectable tie bars that allow the die pad to move relative to the lead frame support structure during encapsulation, preventing direct compressive force on the IC die and maintaining exposure of the heatsink for heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If compressive force is applied by the molding tool during encapsulation to prevent molding compound from seeping between the heatsink and mold chase, then the heatsink remains exposed for heat dissipation, but the IC die may suffer physical damage such as cracking
Solution Approach 1:
The lead frame is segmented into multiple functional components: die pad, tie bars, and support structure. The tie bars act as independent elements that can deflect under compressive force, isolating the die pad from direct force transmission while maintaining heatsink exposure.
Solution Approach 2:
The tie bars are designed with deflectable geometry that allows them to dynamically respond to compressive forces during encapsulation. This dynamic deflection enables the die pad to move relative to the support structure, accommodating molding forces without transmitting them to the die.
2Manufacturing precision
If the molding tool applies compressive force during encapsulation, then molding compound is prevented from covering the heatsink, but the force can cause physical damage to the IC die
Solution Approach 1:
The tie bars serve as intermediary elements between the die pad and the lead frame support structure. During encapsulation, these tie bars deflect to absorb and distribute compressive forces, preventing direct force transmission to the die while maintaining proper heatsink exposure.
3Stability of the object's composition
If the die pad is rigidly fixed to the lead frame support structure, then structural stability is improved, but the IC die is vulnerable to damage during encapsulation and heat dissipation is inhibited
Solution Approach 1:
Different parts of the lead frame have different mechanical properties: the support structure maintains rigidity for overall stability, while the tie bars have controlled flexibility to deflect under load. This local differentiation of mechanical properties allows simultaneous achievement of structural stability and die protection.
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
Prevents physical damage to the IC die while ensuring effective heat dissipation by allowing the die pad and heatsink to move with the compressive force, maintaining the heatsink's exposure and preventing molding compound from covering it.
Implementation Method 1
the tie bars deflect to enable the die pad to move relative to the lead frame support structure
Implementation Method 2
the device may include a heatsink that is mounted on top of the die
Data Source
AI summary
A packaged integrated circuit (IC) device having a heatsink mounted onto an IC die, itself mounted onto a die pad, is assembled using a lead frame having tie bars that deflect during an encapsulation phase of the device assembly, which enables the die pad, the die, and the heatsink to move relative to the lead frame support structure when compressive force is applied by the molding tool. This movement results in negligible relative displacement between the heatsink and the die during encapsulation, which reduces the probability of physical damage to the die. Each tie bar has a number of differently angled sections that enable it to deflect when compressive force is applied to it.