Why is electron beam welding not used for resistance values above 2512 100mR?

Regarding whether electron beam welding technology is used for resistance values of alloy resistors (especially 2512 package size) above 100mR (0.1 Ω), it can be understood as follows:

This is a very common and reasonable approach, especially in applications that require high reliability and power, but it is not absolutely "used for all" as technology is always evolving and alternative solutions exist.

The following is a detailed analysis:

1. Challenge: Heat dissipation issue
In order to achieve such low resistance for low resistance resistors (such as above 100mR), the thickness of the resistance alloy layer must be significantly increased (because the resistance R=ρ L/A, the cross-sectional area A increases and R decreases).
When the alloy layer thickens, in the traditional reflow soldering process, the resistor itself becomes a huge "heat sink".
The enormous heat capacity makes it difficult for solder joints (between terminals and PCB pads) to reach sufficient temperature, resulting in the solder being unable to fully melt, wet, and form a good intermetallic compound layer.
The result is cold welding, virtual welding, or insufficient welding strength, which seriously reduces the reliability and power bearing capacity of the product.

2. Advantages of electron beam welding
High energy density and precise control: Electron beam welding uses high-speed electron flow to bombard the welding area, with extremely high energy density, which can instantly melt the metal.
Deep penetration welding and low heat input: It can form a weld with a large aspect ratio, "nail" the molten metal onto the substrate, and at the same time, the overall heat input is relatively low (heat is concentrated in a very small area).
Solving the heat dissipation problem: It is precisely this high energy density and centralized heating characteristic that can overcome the heat dissipation problem caused by thick alloy layers, ensuring a strong, low resistance, and high reliability metallurgical bond between the terminal and the alloy layer. This combination itself has extremely low resistance and will not become a bottleneck that limits resistance performance or reliability.
High reliability: The formed weld seam has high strength, excellent heat shock resistance, and mechanical vibration resistance, making it particularly suitable for high demand fields such as automotive electronics, industrial control, and power supply.

Why do we say 'universal' instead of 'absolute'?
Cost considerations: Electron beam welding equipment is expensive, the process is complex (requiring a vacuum environment), and the production speed is relatively slow. For cost sensitive applications, manufacturers may seek alternative solutions.
The development of alternative processes:
Special solder/flux/process optimization: Some manufacturers may attempt to solve the soldering problem of thick alloy layers by developing special high-temperature solder, strong active flux, and optimizing the reflow soldering curve (such as higher peak temperature, longer above liquidus time, and localized heating in specific areas). This may be feasible in situations where the resistance is not particularly low (such as close to or slightly higher than 100mR) or where reliability requirements are slightly lower.
Resistance structure design: By changing the design of the resistor (such as designing a heat dissipation path at the bottom of the alloy layer or selecting a substrate material with better thermal conductivity), it may also partially alleviate the welding heat dissipation problem, but this usually increases design complexity and cost.
Other welding techniques, such as laser welding, are also choices for high-energy density welding, but electron beam welding usually has advantages in deep penetration welding and reliability.
Application scenario differences: For consumer electronics products, if the requirements for extreme reliability and power cycle life are not the highest, rigorously validated non electron beam welding processes may be accepted. But for automobiles (AEC-Q200), aerospace, high-end industrial power supplies, etc., electron beam welding is almost the standard requirement for low resistance alloy resistors above 100mR.
Package size: 2512. The package is relatively large, and the heat dissipation problem is more prominent. For low resistance resistors in smaller packages (such as 0805, 1206), heat dissipation issues may not be as severe as 2512, and the possibility of using special reflow soldering processes is relatively higher. However, electron beam soldering is still common for high resistance versions or high reliability requirements.

Conclusion:

Yes, for alloy resistors packaged in 2512, electron beam welding (or other high-energy beam welding such as laser welding, but electron beam welding is more mainstream) is the most mainstream and reliable technical solution in the industry for welding terminals and resistor alloy layers in the resistance range of 100mR (0.1 Ω) and lower. This is a key technology to overcome the heat dissipation of thick alloy layers, ensure welding quality, and ultimately ensure product reliability.
It can almost be considered that in application fields that require high reliability (such as automotive, industrial, etc.), 2512 alloy resistors with a resistance of over 100mR must use electron beam welding technology. Product specifications usually clearly indicate the welding process.
It cannot be absolutely said that 'everything is used' because:
Cost sensitive applications may have validated alternative solutions (special solder/processes).
With the continuous development of technology, new welding methods or materials may emerge.
For situations where the resistance is slightly higher than 100mR (such as 150mR) and the reliability requirements are not extreme, the possibility of alternative solutions is slightly higher.

Simply put, if you see a 2512 alloy resistor with a nominal resistance of 100mR or lower, and it claims to be used for automotive or industrial applications, then there is a high probability that it is using electron beam welding technology. This is one of the key processes in ensuring product performance and reliability in this field. Checking the manufacturer's product specifications or consulting directly with the manufacturer is the best way to confirm the welding process when selecting.