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I'm working on a layout for a PCB and I need to include a handful of pull-up resistors. The board I'm working on will be a proof of concept, and it is likely I will only need one (and order two). That being said, I'd like to keep the board area small. In addition, I'm using through-hole components to make any revisions easy.

For these pull-up resistors, vertically mounting them would save some space and cost instead of alternatively mounting them horizontally. However, I rarely see vertically mounted resistors in commercial or industrial products. So, should I avoid using the vertical resistors even though they will save cost up front?

Upon searching Google for an answer to my question, I came across these two links: http://www.head-fi.org/t/162556/any-reason-why-i-shouldnt-use-resistors-vertically http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=90

The consensus is that vertical resistors are less popular because:

  1. Auto-insertion machines can't (or don't prefer) vertical resistors. This isn't an issue for me since I'll be soldering the board myself.
  2. Horizontal mounting provides more stress relief. This is also no problem since my board will be safe in an enclosure that is only going to get light use to prove a concept.

Are there any other reasons I am overlooking? Granted, most modern designs use SMT components that take up even less space. If the best answer to my particular situation is to just break down and learn to solder the SMT components, I would still like the background knowledge as to why the horizontal resistors are more popular.

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Wanting to use thru hole parts makes no sense. A board with surface mount parts is easier to edit than one with thru hole parts. –  Olin Lathrop Mar 5 at 15:20
    
@OlinLathrop Also, he probably doesn't see a lot of vertically mounted through-hole resistors probably because this is a space-saving technique. But if space is so generously available that a through-hole PCB can be used, then why bother with vertical resistors ... –  Kaz Mar 6 at 0:55
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To clarify, using through-hole components is easier for me specifically since I haven't worked with hand soldering any SMT components before. Not for long now though. –  jrtrzeciak Mar 6 at 1:20
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5 Answers 5

up vote 13 down vote accepted

Mounting a resistor vertically creates a bigger loop that can pick-up interference magnetically. Compare this with a resistor being mounted on the PCB flat against a flooded ground-plane. The voltage pick-up level is proportional to frequency and area of loop formed by the resistor. This is why surface-mount resistors are preferred a lot of the time.

Also, A high value resistor mounted vertically is also asking for trouble in the presence of HF electric fields - what you can create is a mini-antenna.

As for pull-ups and downs, surely you won't be swapping these out in your prototype - I'd consider using surface mount devices for these parts.

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I accepted this answer since it most directly answered my question (e.g. more potential issues that I overlooked), but all responses were helpful. It looks like for my application, I will be alright with vertical resistors. However, I'm now going to come up with a small project to do at home to practice soldering SMT components. It's now very clear that it will be an invaluable skill, and something that can be done by hand, not just pick and place machines. Thank you all! –  jrtrzeciak Mar 6 at 1:14
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Mounting resistors vertically is something that you can find even in high-quality old equipment.

This photo shows the main PCB of a Fluke 27 DMM. It was taken by Dave Jones of EEVBlog. The date code on the ICs suggests it was made in 2004/5. enter image description here

These were designed to for industrial use. (e.g. in mines with potentially explosive atmospheres and by military forces) it seems that vertical mounting isn't necessarily unable to withstand a fair amount of vibration and shock. I have a more than twenty year old ex-military Fluke 25 that carries many scars of rough usage and still works very well. There are plenty of these around so I don't think it's an exception.

Here's a photo of the main PCB in my Fluke 25. (Date codes on the IC's suggest it was made in 1988, the PCB is marked 1984 design).

enter image description here
Not a lot changed in 17+ years.

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Good photo showing the lacquer on the leads. –  Spehro Pefhany Mar 5 at 19:18
    
So that's what those big, rotary switches look like. I need to start taking more things apart at home. –  jrtrzeciak Mar 6 at 1:15
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Vertical resistors are a bit messy and can short if they are pushed over. For the same reason they're less resistant to vibration (for example they would probably be inappropriate in an automotive or aerospace application).

In large quantities, vertical resistors are available preformed (bulk or in tape and reel or ammo pack), some even have the long lead dipped in lacquer (like the body) so they can't short as easily. They're still pretty popular in the low end of production, and they can be stuffed by machine. Photo here: enter image description here

If vibration isn't an issue, there's really little reason why you shouldn't do this, with care to avoid possible shorting. You could always sleeve the long lead if there looks to be an issue.

Keep in mind that in most cases you'll be far better off to use a surface mount resistor. You can start with something huge like 0805 (or even 1206) until you get used to them. Compare sizes here.

SMT resistors sizes I gave above are based in measurements in mils (0805 is 80mils by 50mils or about 2mm x 1.27mm). The metric equivalent of 0805 is 2012. I would NOT suggest that you start with these new Rohm parts, which are metric 03015 (0.3mm x 0.15mm). Several million will fit in a 1" cube, and they are close to being an inhalation hazard.

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Its funny that 0805 is considered HUGE these days ;) However, we use 0805 in most of our products where space isn't that much of a concern because we typically hand solder our prototypes and you can easily read the part value. –  Rev1.0 Mar 5 at 15:40
    
0603 mostly still has part values marked. Below that, nothing. There are also high precision parts available. So, I try to use 0603 mostly these days, but it can't last forever. –  Spehro Pefhany Mar 5 at 15:43
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To answer a question you didn't ask, if you need a few pullup resistors, you will probably save more space and time by using a resistor network such as shown here.

resistor pack

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I did use these when the resistors were close together, but I was still curious for when one or two were off by themselves. –  jrtrzeciak Mar 6 at 1:17
    
This was the answer that popped up in my mind at the first moment I read the posted question. If anyone insists on using THT resistors for pull-up/down, this is the preferred way to go. –  Laszlo Valko Mar 6 at 1:22
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In my experience, vertical resistors are very common in cost-sensitive, hand-soldered products (in other words: cheap products from China). So I think your are making a good decision when cost is a major concern.

But I am a bit surprised that PCB area is a major cost driver in a prototype, especially when there are only two TH resistors?

In my experience hand soldering a horizontal resistor is much easier because they tend not to fall out of the board when you flip the board over, so I prefer horizontal resistors, especially in prototypes!

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Bend the leads and they don't fall out. –  Ecnerwal Mar 5 at 17:22
    
You, but I prefer not to bend in the first place. And bent resitors make an uneven top surface, so IME assembling is easier with horizontal resistors. But YMMV. –  Wouter van Ooijen Mar 5 at 17:57
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