?

 

For those with the skills, SMT is going to be far easier than through hole. No or few holes to drill. Just from your question, it is likely you lack skill for SMT and should probably with through hole for now.

No one method is really any more "reliable" than the other. Through hole was doing very well, lots of years before SMT was developed. Before PCBs there was point to point wiring on a chassis which worked for years.

A good through hole design will beat a lousy SMT design, any day.And a good point to point design will beat a lousy PCB design. Though point to point did suffer from bad connections but that was a more of a question of workmanship. The PCB allowed the circuits to be assembled by a machine rather than a human allowing a higher consistency of quality.

 

I maybe opening up a can of worms here Also Crown used to use a crimped mechanical connection on there pcb because they claimed the crimp was better then a soldered connection? .

You should have gone through the wire wrap era!
Max.

 

You should have gone through the wire wrap era!
Max.

I was there. I had to maintain a system that had 2 - 8"x10" that was all wire wrap. I wish I had kept my wire wrap tool. It had a nice stripper. I still use wire wrap wire on proto boards.

 

Though wire wrap really is a work of art. Very pretty to look at. For some reason it makes a circuit board for a computer look more like it should go into a computer than a PCB to me.

 

I am sceptical of the claim that SMT is more reliable as if you flex the board you can crack the the solder joints on the boards

Flexing any board can cause problems; and not just for solder joints. Unless a board is designed to be flexed, it shouldn't be stressed in that manner.

sometimes when you open up electronics you find components rolling around the case because they got hot then fell off the board.

It's unlikely that it was due to heat. The temperatures required to make parts fall off would be the same required for soldering; around 600-800F.

Also Crown used to use a crimped mechanical connection on there pcb because they claimed the crimp was better then a soldered connection?

Soldered joints shouldn't be used for their mechanical strength.

 

Well I agree that a pcb should not get stressed, however I still have seen my fair share of warped and permanently deformed circuit boards?


Yes I have worked on several pieces where the components will heat up and fall from the pcb, it is enough to boil the solder of the other surrounding components as well. The problem of what would cause the component to heat up is lease of my concern here, I guess where I am going with that is it is much more unlikely for a thru hole component to fall off roll around and ruin other stages or pieces of the circuit?

Thru hole is better for reliability due to the mechanical advantages, but you need to look at the whole system. For example if you have to use 2 boards instead of one. Then you need to factor in contact reliability.
Flexing can also be a problem with surface mount. Not because the component comes off but because it cracks internally.

 

Not 100% clear on your example? Are you saying if the 2 boards are stacked on top of one another or connected with pins?

If you need to get signals from one board to another you will need tome kind of connector. They can have poor reliability.

 

You know I didn't give your comment much thought at first but now it seems obvious, Connectors are the most likely things to have problems in electronics. So I guess my interconnection might be a bigger issue then if I chose to use SMT or thru hole. I have given much thought to audio connectors but not to connections from pcb to pcb??? I usually stick with pin and headers, because it's all I am use to using. However I will follow this down the rabbit hole and see what is the latest and greatest. I do like the idea of soldered connection but that might not work so well on equipment that I am constantly changing or experimenting with. Wire wrapping?!?

Funny you bring the pin and header up. I had a problem once with 3 boards stacked using pin and header. It worked really good but one cap would always go bad - not a lot of failures, but enough to know something was wrong. Turned out to be internal fracture due to pressing the boards together.

 

Just a few thoughts on Reliability in solder connections:

Distribute and over-size hot components like resistors. For instance, use (2) 2 watt resistors instead of a single 3 watt resistor. Mount them above the board so they have more room for convection and radiation. Use extra large copper soldering areas to dissipate the heat. If you have copper on both sides of the board, use it! Go overboard on heat sinks for large transistors. The only thing it's going to hurt is the co$t. Some high ripple current capacitors can get too hot. Put several smaller capacitors in parallel if the circuit can allow the use of the extra physical space required.

Do not solder relays for 3 or more amps to a circuit board. The vibration and the high current cause solder fatigue.

Do not design circuit boards for intentional flexing. Allow for thermal expansion/contraction when designing the mounting brackets.

Conformal coating helps vibration survival.

Keep your wire flexing under control at the board by anchoring the bundle. Let the wires flex in the air space between boards and other anchor points.