Multi-die Sensor Device with Dummy Lead Cavity
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Solution Overview
Problem
Conventional multi-die sensor devices face challenges in protecting bond wires and pressure sensor dies due to narrow process tolerances in Film Assisted Molding (FAM) and compression molding processes, which can damage wires and diaphragms, and require careful control of gel dispensing to avoid damage.
Innovation Solution
The use of a lead frame with normal and dummy leads, where the dummy lead has exposed wire bonding areas to form a cavity during molding, allowing for protection of bond wires and easy electrical connection between dies, and a method involving Pin Assisted or Film Assisted Molding to create an opening that exposes the second wire bonding area of the dummy lead, while encapsulating the first die and bond wires with a mold compound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Film Assisted Molding (FAM) process is used to create opening for pressure sensor die, then the pressure sensor die can function, but the process tolerance is very narrow and bond wires may be damaged
Solution Approach 1:
A gel substance is introduced as an intermediary material between the mold compound and the pressure sensor die. The gel fills the cavity and protects the bond wires and die surface during molding, allowing the FAM process to proceed with relaxed tolerances while maintaining die functionality through the opening.
Solution Approach 2:
The gel is applied to the pressure sensor die before the molding process begins. This beforehand cushioning creates a protective layer that absorbs molding stresses and prevents damage to bond wires and die surface, enabling the molding process to tolerate greater variations in positioning and pressure.
2Reliability
If compression molding process is used to encapsulate dies, then encapsulation is achieved, but die cracking and mold bleeding occur due to tight process windows
Solution Approach 1:
The gel serves as a compliant intermediary layer between the rigid mold compound and the fragile pressure sensor die. This gel layer absorbs and distributes molding pressures, preventing die cracking while also preventing mold compound from bleeding into areas where it should not go, thereby widening the acceptable process window.
Solution Approach 2:
The introduction of gel changes the physical parameters of the molding system by adding a compliant, pressure-distributing layer. This allows compression molding to be performed with less precise control of clamping pressure and die positioning, effectively widening the process window while maintaining encapsulation integrity.
3Reliability
If gel dispensing is performed to coat dies and bond wires, then protection is provided, but the height control must be carefully controlled to avoid damage
Solution Approach 1:
The gel dispensing process is designed to be self-regulating, where the gel naturally flows to cover the necessary surfaces without requiring precise height control. The gel's viscosity and flow characteristics allow it to self-adjust to the die and wire surfaces, reducing the precision requirements for dispensing height while maintaining effective protection.
4Reliability
If large amount of gel is used to coat dies and bond wires, then complete coverage is achieved, but material usage increases
Solution Approach 1:
Instead of uniformly coating all surfaces with gel, the process applies gel selectively to critical areas where protection is most needed, such as bond wire connection points and pressure sensor die surfaces. This localized application maintains protective coverage where required while minimizing overall gel consumption.
Data Source
AI summary
A semiconductor device includes a lead frame having a flag and leads that surround the flag. The leads include a dummy lead that has first and second wire bonding areas. A first die is attached on the flag and electrically connected to the first wire bonding area. The first die and the first wire bonding area are encapsulated with a molding material and a cavity with an opening is formed above the first die. The second wire bonding area is exposed in the cavity. A second die is placed in the cavity and electrically connected to the second wire bonding area such that the second die is electrically connected to the first die by way of the dummy lead.