Cold-Welded Pillar Contacts With Lateral Pressing for Power Semiconductors
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Solution Overview
Problem
Existing connection technologies for power semiconductors, such as wire bonding, sintering, and pressure contacts, face issues like damage from forces, thermal stress, electrical interference, high manufacturing effort, and potential damage from constant pressure, which are not adequately addressed.
Innovation Solution
A method using a specially shaped pressing tool with formations that promote lateral deformation of pins or pillars, reducing compressive load on the semiconductor and facilitating cold welding with reduced risk of cracking, and incorporating a metallic buffer layer for improved force distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wire bonding is used to create electrical connections on the top side, then electrical connections can be established, but forces are exerted during connection creation which can damage the semiconductor component and local temperature increases occur during operation
Solution Approach 1:
The patent replaces the mechanical wire bonding process with a cold welding process using a pressing tool. The pressing tool applies controlled pressure to create direct metal-to-metal contact between the contact element and the semiconductor contact surface, eliminating the need for wire bonding and associated mechanical damage and thermal stress.
Solution Approach 2:
The patent changes the connection parameters by using a pressing tool with specifically designed pressing surfaces that distribute force evenly across the contact area. This prevents localized high forces and temperature increases while maintaining reliable electrical connection.
2Temperature
If sintering processes are used instead of wire bonding, then flat connections with significantly larger cross-sections and higher temperature resistance are achieved, but high manufacturing effort and high pressure are required
Solution Approach 1:
The patent uses a simple pressing tool that can be easily manufactured and replaced, avoiding the complex sintering equipment required for traditional sintering processes. The pressing tool creates reliable connections without requiring high-temperature sintering equipment or complex manufacturing setups.
Solution Approach 2:
The patent changes the process parameters from high-temperature sintering to controlled cold pressing. The pressing tool applies sufficient pressure at room temperature to create reliable electrical connections, eliminating the need for high-temperature processes while maintaining connection quality.
3Object-affected harmful factors
If pressure contacts are used to replace bonded connections, then thermal stresses are avoided, but forces are permanently exerted on the semiconductor which can damage the component over time
Solution Approach 1:
The patent designs the pressing tool with specifically shaped pressing surfaces that concentrate force locally on the contact area while distributing it evenly across the contact interface. This localized force application creates reliable electrical connection without exerting damaging permanent pressure on the semiconductor structure.
Solution Approach 2:
The pressing tool applies force temporarily during the connection process to create the electrical bond, then releases the pressure. This preliminary action establishes the connection without leaving permanent damaging forces on the semiconductor component.
4Object-affected harmful factors
If flat contacts are used, then thermal stress is reduced, but perfectly flat surfaces are required and sliding contacts must remain permanently free of contamination and oxide layers
Solution Approach 1:
The pressing tool creates localized contact points with controlled geometry, eliminating the need for perfectly flat surfaces across the entire contact area. The pressing surfaces are designed to accommodate minor surface irregularities while maintaining reliable electrical connection.
Solution Approach 2:
The pressing process creates a permanent metallurgical bond through cold welding, eliminating the need for sliding contacts that must remain free of contamination. The connection is established in advance and does not require maintenance of surface cleanliness during operation.
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 method minimizes the risk of semiconductor damage, reduces thermal stress, and enhances the reliability and mechanical security of the connection while maintaining low contact resistance, effectively addressing the limitations of previous technologies.
Implementation Method 1
The pins are inserted into through openings of a contact of another element or conductor and cold-welded to them
Implementation Method 2
The formations promote lateral deformation of the selected pins with respect to a pressing direction during the pressing process
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3A~3C
AI summary
The present invention relates to a method for establishing an electrical connection between a circuit element (110, 210, 310) (e.g., a semiconductor element such as a power semiconductor device) and another element (or conductor). In this process, an electrical contact (111, 211, 311, 120, 220, 320) with a planar section (112, 212, 312, 122, 222, 322) is first provided on the circuit element (110, 210, 310) and on the other element.Furthermore, several pillars (113, 213, 313) made of conductive material are provided on the planar section (112, 212, 312) of one of the contacts (111, 211, 311), as well as corresponding recesses (121, 221, 321) made of conductive material on the planar section of the other contact (120, 220, 320). The conductive material of the pillars (113, 213, 313) and the conductive material of the recesses (121, 221, 321) are selected to be cold weldable. The recesses (121, 221, 321) are provided as through-holes, and the pillars (113, 213, 313) are formed so that, after being fully inserted into the passage openings (121, 221, 321) protrude on the other side of the passage openings (121, 221, 321).The pins (113, 213, 313) are inserted into the through-openings (121, 221, 321) and cold-welded together by at least partially pressing the pins (113, 213, 313) in the through-openings (121, 221, 321) using a pressing tool (130, 230, 330), which has features (131, 231, 331) for at least selected pins (113, 213, 313) that promote lateral deformation (140A, 240A, 340A, 140B, 240B, 340B) of the selected pins (113, 213, 313) with respect to a pressing direction (132, 232, 332) during the pressing process and This results in lower compressive stress on the element (110, 210, 310) supporting the pins (113, 213, 313). Since the pressing force already has lateral components at the beginning of the pressing process, the load in the direction of the switching element (110, 210, 310) is avoided or reduced.The projections (131, 231) can act at least approximately on the cross-sectional centers of the selected pins (113, 213), whereby the pins (213) can additionally be formed hollow, so that the hollow pins (213) have blind holes which have smaller cross-sectional dimensions than the projections (231) of the pressing tool (230) and into which the projections (231) of the pressing tool (230) partially engage at the beginning of the pressing process. Alternatively, the projections (331) between each of the selected pins (313) can act on the material of the contact (320) with the through-holes (321), wherein the contact (320) with the through-holes (321) can additionally have material recesses (323) in the areas between the through-holes (321), which are formed on the side of the contact (320) facing away from the planar section (322) and on which the projections (331) of the press tool (330) act.The pins (113, 213, 313) and the corresponding through-holes (121, 221, 321) can be arranged in a grid, preferably in a square grid. In all embodiments, the circuit element (110, 210, 310) can have pins (pillars) (113, 213, 313) on two opposite sides, which are electrically contacted in a single step by pressing the pillars (113, 213, 313) into corresponding openings (121, 221, 321) of contacts (120, 220, 320) from both sides.