Lead spacing for through hole resistor

What power rating / body size ?

There's accepted practice.

IPC2220 ? Hmm. hadn't heard of that before.

Graham

It depends on the package body size. Search some manufacturers websites and datahseets and see if you can find a suggested footprint or land pattern.

For through hole resistors, I usually try to keep the spacing to a .100" increment (.200", .300", etc) depending the size. I try to maintain some measure of a grid spacing and alignment to keep things neat, though this is sometimes difficult.

Another consideration is I try to standardize the hole sizes as much as possible because the more different hole sizes you have means more drill changes are needed which equates to more cost.

IPC deals mainly with SMDs. I use 0.4" for 1/4 W resistors, I think that most people do.

Leon

Or maybe 10mm.

Best regards, Spehro Pefhany

I'd allow approx 2mm per lead extra over the body length for the lead forming machine. see data sheet here

martin

.20 is the standard. You can lay them down and bend the leads to fit whatever space available, or you can bend one lead 180 degrees and insert both leads within the .100 or .200 spacing on the PC board as long as you have height space.

It is ? Most ppl use 0.4" IME or 0.3" for 1/8W to save space.

I wouldn't recommend vertical mounting.

Graham

On Sat, 03 Jun 2006 08:12:34 +0100, Pooh Bear Gave us:

That depends on whether it is a fixed or mobile application.

If mobile, it is still OK if the item gets encapsulated or conformally coated as well.

They actually dissipate their heat better as well.

The silk screen is nicer too. A simple circle with a little dash pointing toward the other hole connected to the circle perimeter.

The ONLY problem I can think of that vertical axial leaded resistor mounting has is in automated production cycles. It typically causes a few insertion failures or solder cycle failures or a few sorts.

There is absolutely nothing wrong with the practice from an electrical POV, however.

I've had to use it on occasion, to get a board to fit a specified enclosure. I can't think of any reasons not to do it for hand-assembled boards, especially for amateur radio applications which is when I have used it.

Leon

Think of the stress on the mechanical solder joint esp wrt single sided boards.

Graham

Where does the stress come from?

Leon

--- I don't think so. Horizontally mounted, the leads are short and sunk to a pad/trace which helps with conducting the heat out of the center of the resitor. Also, the entire horizontal surface is radiating and convecting heat away from the resistor body.

Mounted vertically, only one lead is mounted close to a pad. The other one and the body of the resistor catch the heat that's being convected upward with the result that there's a temperature gradient generated which will make the resistor progressively hotter as its apex is approached. As a result, part of the resistor will be hotter than if it were horizontally mounted.

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--- See above.

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--- If the dissipation is miniscule, I agree.

But, if the resistor is dissipating a sizable fraction of its rating I'd be leery of mounting it vertically without getting some temperature data.

-- John Fields Professional Circuit Designer

On Sun, 04 Jun 2006 09:58:25 -0500, John Fields Gave us:

True, but that is via conduction. I was referring to radiated dissipation.

So is the entire vertical surface. In fact, the horizontal surface has a fiberglass low thermal conduction PCB which it is against that will negate some of its radiating capacity.. even blanketing the part and slowing the dissipation of its heat.

Cement bathtub type power resistors are mounted vertically all the time (read quite often) for this reason, and for the reason of not wanting to burn up said fiberglass based PCB assembly.

On Sun, 04 Jun 2006 09:58:25 -0500, John Fields Gave us:

IR heat radiates outward and the temp at the bottom of the ceramic cylinder in the resistor will be a mere few degrees cooler than the top, at best.

Why is it then, that in practice, they are not?

Even an IR imager proves it.

For a properly designed assembly. If one actually designs near the resistor's declared capacity, heat is going to be an issue regardless of how the device is mounted. If one designs in the component such that it does NOT get anywhere near it's rated upper end, it will always be cool enough for either mounting fashion not to be a problem.

The mere difference of heat conducting down a body length wire to the PCB connection, and it being right there at the resistor body are very near negligible as well.

On Sun, 04 Jun 2006 09:58:25 -0500, John Fields Gave us:

In either vertical OR horizontal mounting (without a reasonable space between it and the PCB), I would say that one should be leery of either choice.

Hundreds of millions of portable transistor radios were made with most of the axial-lead components mounted vertically on the cheapest paper-based phenolic boards. They were pretty reliable.

Best regards, Spehro Pefhany

That kind of stuff used resistors that had 'enamelled' leads to prevent inadvertent shorts and a kinked lead to help relieve the mechanical joint at the pcb.

Graham

the

I've got an old BT ( actually Post Office Telecommunications ) modem somewhere that has many of the components mounted in stress relieving cradles. Some even have a stress relief loop on the leads !

Graham

Oh, but that high tech stuff came later. The early ones often had plastic tubing on the leads, or nothing at all.