I designed PCB boards to take a minimum of square mm in area using through hole components. Specifically TO-22 2N7000s and 1/4 W resistors.

I don’t need 1/4W, just had them on hand. I’ve since obtained 1/8 W resistors. They don’t quite fit horizontally but I’d like to use the existing PCBs.

I’ve sketched out how I see forming the 1/8 W leads. There is sufficient horizontal room to fit them as in my sketch (on the back of my restaurant receipt) below. A is the 1/4 W placement; B is what I’m thinking.

Any issues? I don’t think so… but what do I know?

 

I've never seen B in use but quite often see and use A. FWIW The problem with A is that flipping and handling the PCB while soldering all of the components, A tends to get bent down and has to be straightened in final assembly.

 

I've never seen B in use but quite often see and use A. FWIW

I’ve never seen B either, but it preserves my not insignificant investment in PCB boards. That’s why I asked.

 

You do what you gotta do.

 

I've never seen B in use but quite often see and use A. FWIW The problem with A is that flipping and handling the PCB while soldering all of the components, A tends to get bent down and has to be straightened in final assembly.

Same, I like the A with the leads formed so the component is vertical in the case of resistors. I vote for A.

Ron

 

If I understood correctly, Figure A is how you currently have 1/4 W resistors mounted, right? If so, why can't you place the 1/8 W resistors the same way? Or is it that you could, but are thinking that B might be a better alternative?

If the latter, I would recommend against it unless there is some significant advantage to reducing the component height (or if it would improve the parasitics in a design that is sensitive to them).

If you stick with A, be sure to orient the resistors consistently (if you aren't already doing that). The normal convention is to put the tolerance band at the bottom.

 

If I understood correctly, Figure A is how you currently have 1/4 W resistors mounted, right? If so, why can't you place the 1/8 W resistors the same way? Or is it that you could, but are thinking that B might be a better alternative?

Sometimes, you just can’t see the forest for the trees. Of course, I can form the 1/8 W resistors as in A. My thought process was to reduce the height when 1/4 W resistors are used. Forming the 1/8 W resistors in the same way WILL accomplish that goal.

The limiting factor is the height of the mounted TO-22 2N7000s. I had an issue when multiple PCBs were mounted horizontally and the resistors could short to the board above. (The PCBs are meant to be modular and the number required depended on the specific installation).

With the combination of 1/8 W resistors and the 2N7000s, this problem is minimized. The total area is thus minimized and this is a very good result.

Thanks for your observation, @WBahn !

 

If you stick with A, be sure to orient the resistors consistently (if you aren't already doing that). The normal convention is to put the tolerance band at the bottom.

There is a definite pattern of stating personal opinions as rules that absolutely must be followed here.

Wiring both ends of a CAT5 cable to either 568A or 568B on both ends? A rule that allows the cable to work. All the resistors same end up? Satisfies your OCD but makes no difference to the circuit board.

 

There is a definite pattern of stating personal opinions as rules that absolutely must be followed here.

Wiring both ends of a CAT5 cable to either 568A or 568B on both ends? A rule that allows the cable to work. All the resistors same end up? Satisfies your OCD but makes no difference to the circuit board.

Have you never heard of the concept of "best practices"? It was a suggestion, not a rule that absolutely must be followed. The idea is to be considerate to anyone -- including themselves -- that ever needs to examine the components on that board in the future. Has nothing to do with OCD. It is in the same category of orienting silkscreen labels the same way on a PCB so that they can be easily read without have to constantly turn the board or mentally rotate and/or flip them when you read them. These practices not only make working the boards more convenient and time efficient, it also reduces the likelihood of making mistakes. If you see no value it adopting practices that make things easier and reduce the chances of making easy-to-avoid mistakes, then by all means don't adopt them. But do you find them so objectionable that you must complain when other people suggest them?

 

The only drawback I see to "A" is the long length of exposed lead that could short to another like resistor. So to be proactive one could add a length of sleeving to prevent such a short.

This is the saecond time this week I've seen & posted on such a mounting method that I have always known as "Japanese TV style. That's not a slight, it is an accurate description of how Japanese TVs were once assembled on single sided PCBs.

 

Transistor radios, too. Plenty of consumer electronics things were built that way to minimize board space. A nightmare to work on, though.
As for OCD and board layout, ideally you also place all the semiconductors and polarized caps so they're all in the same orientation. It makes stuffing easier and prevents errors, more so if there's no silkscreen overlay. Maybe not possible with SMD, RF, and high power stuff.

 

There are flaws with both "A" and "B", which are vibration susceptability leading to lead failure. So neither one is correct for applications where there will be vibration encountered, unless the assembly is encapsulated with some compound. In addition, "B" is likely to suffer automated assembly problems,, although with hand assembly it could work. So for non-vibration applications "A" would be the preferred bending scheme, although there is the very real possibility of damage when the component is forces over flat, after the board is soldered. That also happens with tall thin electrolytic capacitors a lot. They become open circuit when folded sideways. Difficult to diagnose.

 

So to be proactive one could add a length of sleeving to prevent such a short.

I still have several values of 1/4W resistors with preformed leads for vertical mounting. On those, the long lead is coated with the same material as the resistor body for insulation. You used to be able to find manufacturing surplus easily. A quick search didn’t turn up anything now—but it was a very quick search.

I used to spend time cutting and threading spaghetti sleeving onto the lead of resistors I was mounting like this, but then I realized that a properly sized piece of heat shrink will easily fit over the whole thing, faster and easier. You don’t have to shrink it unless the tube you have isn’t a snug fit.

 

There are flaws with both "A" and "B", which are vibration susceptability leading to lead failure. So neither one is correct for applications where there will be vibration encountered, unless the assembly is encapsulated with some compound. In addition, "B" is likely to suffer automated assembly problems,, although with hand assembly it could work. So for non-vibration applications "A" would be the preferred bending scheme, although there is the very real possibility of damage when the component is forces over flat, after the board is soldered. That also happens with tall thin electrolytic capacitors a lot. They become open circuit when folded sideways. Difficult to diagnose.

These are 1/8w resistors so about 1/4 the mass and 1/2 the height of a "typical" THT resistor so the vibration concern is non-existent. There are lots of examples of standing resistors in consumer products (appliances, Musial instruments and alarm clocks for sure). And, as Y points out above, some were sold pre-folded. When I do it, I am just cautious to make sure supply voltage passes through the resistor so there is some resistance in care chassis touches the top of the standing resistor. I never had the patience to insulate them.

 

there's the photo.

 

I've never seen B in use

I have. It is common in power supplies (and old TV's) to elevate hot parts above the pc board to prevent scorching. Often there is an extra little kink in the wires to hold the part in place before soldering. My cut-bend tool had something like this as an option.

I found this image from a similar tool vendor on the innergoogle.



ak

 

Those I've seen but not horizontal where the through holes are closer than the width of the resistor like in DJs B diagram. That's when I see the vertical mounting.

 

Evidently nobody else has ever done anything subject to constant vibration.

 

Evidently nobody else has ever done anything subject to constant vibration.

Or their applications aren’t subject to constant vibration. In the case where there is vibration, your comments are useful.

 

I use 'A' style a lot for tight projects like this:


PCBs about 1" wide, and 1.5" high each. Used _every_ via space on at least 1 of them.