Electronic – Why did Axial Capacitors Fall Out of Use in the Industry


When inspecting the boards from electronics made in 1980s and earlier, one distinct feature is the extensive use of axial, electrolytic capacitors as power supply filter. Axial ceramic decoupling capacitors were used as well, to a lesser extent.

For example, this is a C64 motherboard.

One part of a C64 motherboard, shows 3 large axial electrolytic capacitor at the power regulator section.

Source: Wikimedia Common, by Gona.eu, license: CC BY-SA 3.0

This is a Tektronix 1720 vectorscope board.

One part of a Tektronix 1720 vectorscope motherboard, showing a Signetics 8051 microcontroller, surrounded by axial ceramic decoupling capacitors and axial electrolytic capacitors.

Source: Flickr, by Toby Thain, license: CC BY-NC 2.0

However, although they are still being manufactured, it seems that axial capacitors largely disappeared in most devices since the 90s. Almost none of electronic devices we commonly see have a single axial capacitor. And it's certain that one is going to find something similar to this in a modern device…

The power supply board from a Tektronix MDO4000 mixed-signal oscilloscope, a lot of radial electrolytic capacitors are visible
Source: Wikimedia Common, by Dave Jones from Australia, license: CC BY 2.0


Why did Axial Capacitors Fall Out of Use in the Industry? I can imagine that axial capacitors were optimized for point-to-point wiring back in the pre-PCB era, not PCB assembly, and that the introduction of SMT was another shot. But it was just my imagination, backed by nothing. What were the exact sequence of events and/or rationale that led to the disuse of axial capacitors?

Best Answer

PCB area.

Axials pre-dated PCBs, their construction was ideal for wiring to tag strips and valve bases, and they were adopted for PCBs because that's what was available.

Example of tag strip construction below.

(There WERE radial caps in the valve days : they were generally designed for chassis mounting via a ring clamp, and had tags rather than wire leads. The round object bottom centre is the base of one such capacitor)

enter image description here

It's actually quite surprising they lasted as long as they did alongside radials, into the 1980s.

Radials use much less PCB space, and standing axials on end is a poor compromise, with a long exposed lead (or the added assembly step of sleeving it) as well as being much less robust.