# Any way to surface mounting a through-hole resistor?

I need to solder a 2W through-hole Resistor on one side of pcb, mean like smd component but this is for through-hole resistor. I google and found there is a way call ZI-form, image is below. So is this possible? Any problem with this solution? Is there any way else better?

Thanks very much

• Nice find! I have used something similar in my hobby projects, but I didn't know one could even order resistors pre-formed like this. – Richard the Spacecat Aug 14 '19 at 8:37
• I was lucky enough to to visit NASA a few years ago and got to see some of their PCB assemblies. These had a solid metal base with PCB material on top. This makes conventional through-hole imposable. As a result most of the components were conventional surface mount but I did see a few that were conventional through-hole components with the legs suitably bent to surface mount. – Warren Hill Aug 14 '19 at 10:00
• I would have just gull winged the lead. Does that not work? – DKNguyen Aug 14 '19 at 13:45
• Something like that. Be sure that the bend distance meets spec. This is just as true when used through hole, but the temptation here is to fold them down directly out of body. While that may work perfectly well, there will be a minimum distance to be met. Stress loading on a resistor body when bending is not usually critical but there will be a spec - "proper" bending will involve support in some manner and stress free bending. For some components this is utterly crucial. eg glass encapsulated reed relays tend to fracture at the lead-glass interface if not properly bent. .... – Russell McMahon Aug 15 '19 at 2:53
• ... A must for inclusion in a manufacturing spec. Ask me how I know :-). It WAS in the spec and largely followed (100,000+ products) , but the occasional failure suggested they sometimes "Sailed a little close to the wind". – Russell McMahon Aug 15 '19 at 2:54

Yes, it's possible. If it happens, it must be true.

One problem is the need to form the leads like that. Another is the large weight of the component on potentially small lands, this risks ripping the pads from the board if there are large vibration forces.

Consider instead an array of low power SMD resistors. Apart from being a standard component, these may have another advantage that you can spread them out or interleave with other components to lose the heat better.

A common technique where you need a high voltage resistor is to use several in series. Resistors do share their voltage drop nicely, unlike rectifier diodes or capacitors. It's sensible to make all the resistors equal, then the power and the voltage drop is shared equally. For instance, if you have 5 equal resistors, then each sees 20% of the total power, and 20% of the total voltage drop.

• Or, just get a 2W surface-mount resistor. They're out there, and they work. They cool the resistor by conduction to the pads, so you do need to size the pads correctly -- but that doesn't keep them from working. – TimWescott Aug 14 '19 at 16:17
• Because my case, the resistor work with 230VAC and in my local area, it's hard or expensive to find or buy a small amount of 2W or any SMD Resistor that have rated voltage 350V. Thanks – Ngô Hữu Nam Aug 15 '19 at 2:31
• @NgôHữuNam In that case, a series string of low power low voltage resistors is exactly the thing to use. I've updated my answer. You would have got this answer 24 hours earlier if you'd said 'high voltage' rather than 'high power' as the reason for using a special resistor. – Neil_UK Aug 15 '19 at 5:43
• @NgôHữuNam If all the resistors are equal, then it's just the total voltage divided by the number of resistors. And each resistor in a string of N needs to be 1/N of the total resistance you need. – Simon B Aug 15 '19 at 7:23
• @NgôHữuNam I've updated my answer to include the bit about equal resistors. However, if you are having to ask this sort of stuff, then you ought not to be connecting anything to mains, you are a danger to yourself and others. – Neil_UK Aug 15 '19 at 7:48