Leadless Semiconductor Package with Embedded Electroplated Layer
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Solution Overview
Problem
Conventional leadless semiconductor packages face issues with electroplated layer damage during shipping, handling, and storage, and inadequate adhesion between the leadframe and encapsulant, leading to potential electrical shorts and separation of inner leads due to thermal cycles.
Innovation Solution
A leadless semiconductor package design featuring a half-etched leadframe with integrally connected leads and outer pads, where the encapsulant has cavities to embed the electroplated layer and enhance adhesion, and a manufacturing process involving two etching steps to expose outer pads for secondary electroplating, eliminating the need for solder masks and improving protection and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electroplated layer is plated on the exposed surfaces of the inner leads after encapsulation, then corrosion resistance and soldering adhesion are improved, but the electroplated layer is easily damaged during shipping, handling, and storage
Solution Approach 1:
The electroplated layer is formed on the outer pads before encapsulation, and the encapsulant is then molded to embed and protect this layer. This preliminary plating action allows the electroplated layer to be positioned within the encapsulant structure, where it is protected from mechanical damage during subsequent handling and shipping, while still maintaining its corrosion resistance and soldering adhesion properties.
Solution Approach 2:
The electroplated layer is nested within the encapsulant structure, where the encapsulant material surrounds and protects the electroplated layer. This nesting arrangement allows the electroplated layer to be embedded in the encapsulant, providing mechanical protection while maintaining its functional properties for corrosion resistance and soldering.
2Reliability
If the electroplating is performed after encapsulation, then the electroplated layer can be formed on the bottom surface of inner leads, but the electroplated layer protrudes from the bottom of the encapsulant making it vulnerable to damage
Solution Approach 1:
The electroplating process is performed before encapsulation, allowing the electroplated layer to be formed on the outer pads while they are still exposed. The encapsulant is then molded to embed this pre-formed electroplated layer, protecting it from mechanical damage during subsequent handling and shipping while maintaining its corrosion prevention functionality.
Solution Approach 2:
The encapsulant acts as an intermediary structure that embeds and protects the electroplated layer. By forming the electroplated layer first and then using the encapsulant to surround it, the encapsulant serves as a protective intermediary that shields the electroplated layer from mechanical damage while allowing it to maintain its corrosion prevention properties.
3Ease of manufacture
If the bottom surfaces and sides of the inner leads are exposed from the encapsulant, then the electroplating process can access these surfaces, but there is not enough adhesion between the leadframe and the encapsulant
Solution Approach 1:
The electroplating process is performed before encapsulation when the outer pads are fully exposed and accessible. After electroplating, the encapsulant is molded to embed the electroplated outer pads, providing sufficient surface area for adhesion between the leadframe and encapsulant, thereby preventing separation during thermal cycles while maintaining ease of electroplating.
Solution Approach 2:
The electroplated outer pads serve a dual function: they provide corrosion resistance and soldering adhesion, and they also serve as the bonding interface between the leadframe and the encapsulant. By combining these functions into a single integrated structure, the design achieves both electroplating accessibility and sufficient adhesion strength.
4Reliability
If the electroplated layer is formed on exposed outer pads before encapsulation, then the encapsulant can embed the electroplated layer to prevent damage, but additional etching steps are required
Solution Approach 1:
The etching process is divided into two separate steps: a first etching step that creates initial cavities or recesses in the encapsulant, and a second etching step that refines the cavity shapes and sizes after encapsulation. This segmentation allows the electroplated layer to be formed before encapsulation and then properly embedded, providing protection while managing the complexity of the overall manufacturing process through structured, multi-step fabrication.
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 solution effectively prevents damage to the electroplated layer and enhances adhesion between the leads and encapsulant, ensuring reliability during handling and thermal cycles without compromising cost or thermal conductivity.
Implementation Method 1
The encapsulant has a plurality of cavities reaching to the outer pads to accommodate the electroplated layers
Implementation Method 2
an electroplated layer is plated on the exposed surfaces of the inner leads such as nickel/gold, tin, or solder to prevent corrosions
Implementation Method 3
to enhance soldering adhesion to external printed circuit boards
Implementation Method 4
to enhance the adhesion between the leads and the encapsulant
Data Source
AI summary
A leadless semiconductor package with an electroplated layer embedded in an encapsulant and its manufacturing processes are disclosed. The package primarily includes a half-etched leadframe, a chip, an encapsulant, and an electroplated layer. The half-etched leadframe has a plurality of leads and a plurality of outer pads integrally connected to the leads. The encapsulant encapsulates the chip and the leads and has a plurality of cavities reaching to the outer pads to form an electroplated layer on the outer pads and embedded in the cavities. Accordingly, under the advantages of lower cost and higher thermal dissipation, the conventional substrates and their solder masks for BGA (Ball Grid Array) or LGA (Land Grid Array) packages can be replaced. The leads encapsulated in the encapsulant have a better bonding strength and the electroplated layer embedded in the encapsulant will not be damaged during shipping, handling, or storing the semiconductor packages. Furthermore, the manufacturing processes include two half-etching steps to form the half-etched leadframe where a second half-etching step is performed after forming the encapsulant and before forming the electroplated layer.