Lead Frame Pad Oxide Layer Solder Overflow Control
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Solution Overview
Problem
In electronic component devices using lead frames, the flow of solder beyond the pad area during reflow heating can cause positional misalignment and electrical shorts or opens due to the wettability of solder on copper electrodes, leading to unstable connections.
Innovation Solution
A lead frame structure is developed with a metal oxide layer surrounding the pad area, which reduces the active force of the flux and prevents solder from flowing outward, ensuring the solder remains within the pad area for stable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the copper electrode surface is exposed around the pad part, then the solder wettability is improved and solder can flow out to surround the pad part, but the solder flows outward from the pad part causing the power semiconductor chip to be tilted or mounted with positional misalignment and electric short or open may be caused
Solution Approach 1:
The copper electrode surface is segmented into two distinct regions: a pad part with exposed copper surface for solder attachment, and a surrounding region covered with metal oxide layer to prevent solder overflow. This segmentation allows different functional requirements to be met in different areas.
Solution Approach 2:
Different surface properties are applied to different locations: the pad part has high wettability (exposed copper) to attract and hold solder, while the surrounding region has low wettability (metal oxide covered) to repel solder and prevent overflow. This local differentiation solves the contradiction between needing solder attachment and preventing solder spread.
2Reliability
If the flux actively removes oxide layers during reflow heating, then the solder wettability is enhanced, but the solder flows out to the surrounding region causing positional misalignment and electrical defects
Solution Approach 1:
The metal oxide layer is pre-formed on the surrounding region before soldering to counteract the flux's oxide-removing action. During reflow, the flux attempts to remove the oxide layer and enhance wettability, but the pre-existing metal oxide layer resists this action, preventing solder from flowing into the surrounding region and maintaining mounting alignment.
3Reliability
If the pad part is formed by metal plated layer on copper electrode, then the electrical conductivity is improved, but the solder may flow out to the surrounding region of the pad part
Solution Approach 1:
The metal oxide layer acts as an intermediary barrier between the solder and the surrounding copper electrode region. It allows the pad part to maintain good electrical conductivity through the metal plated layer on copper, while the metal oxide surrounding region mediates to prevent solder overflow, thus protecting against harmful solder spread.
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 solution effectively prevents solder flow beyond the pad area, ensuring reliable connections and preventing electrical shorts or opens, thereby improving the reliability and stability of the electronic component device.
Implementation Method 1
the flux reduces the first metal oxide layer having a predetermined thickness around the pad part, so that an active force of the flux is decreased
Implementation Method 2
The flux has a function of securing the wettability of the solder by removing a natural oxide film on a surface of a metal layer
Implementation Method 3
the wettability of the solder is secured on the copper electrode around the pad part, as well, and the solder flows out to the surrounding of the pad part
Data Source
AI summary
An electronic component device includes a first lead frame having a first connection terminal and an electronic component. The first connection terminal includes a first metal electrode, a first pad part formed on an upper surface of the first metal electrode and formed by a metal plated layer, and a first metal oxide layer formed on an upper surface of the first metal electrode in a surrounding region of the first pad part so as to surround an outer periphery of the first pad part. The electronic component has a first terminal part provided on its lower surface. The first terminal part of the electronic component is connected to the first pad part of the first connection terminal via a metal joining material.