Wire to Board Solder Joint Reliability

Hello,

I am wondering if anyone on this board has come across literature, or has experience with determining the reliability / durability of wire to board solder joints. I am currently working on an industrial design for a headphone. I need this information to determine which connections require strain relief (maybe a tyco connector) and where I can get away with just soldering a wire to the board directly.

Thanks.

-Brian

Hi, all that you need is industrial standarts. Your choice will depend on most likely vibration conditions. It's not good idea to solder wire to board straight away. better to use special rivets, mount them on pcb, solder them, then solder wire to rivet

You need to avoid any movement of the wire at the solder joint.

Hi,

For a headphone it must be lightweight, flexible, portable.
In that sense you may straightly solder the wire to the board. But wire must be guard against sharp bends; also use best solder for the board

You still require strain relief on the cable, so that between the strain relief and the solder joint there is NO movement of the cable. Any movement will cause a failure of the solder joint or the wire snapping at this point, where it goes from flexible cable to a rigid joint on the PCB. This is even more critical for lead free assemblies as the joints are even more suseptable to repetative strain failures.

Thank you all for the responses. Does anyone have a suggestion for molex type headers that are low cost and would be suitable for my kind of application?

At the moment our headphones are designed to survive one year of wear and tear at the most. Since our company is moving into the consumer electronics space, the warranty itself is two years and we would aim for the product to last significantly longer than that.

Another question: if I wanted to use some type of glue to hold the wire in place, what type of glue would you recommend? Are there any concerns with different types of glue reacting to solder joints over a long period of time?

I am very new in this area of design so any feedback on the above would be greatly appreciated.

-Brian

Simplest method of strain relief I've seen is a knot in the wire that stops it being tugged through a hole in the casing, from that there are several methods, from moulding pegs or special openings in the case, using grommets, low pressure moulded features on the wire, screw down clamps...
Glue, generaly hot melt glue can be used, or silcone.

As for connectors, there are so many out there, by so many companies... Depending on the price of the product being designed will have a big inpact on where I'd look for connectors, and predicted volumes. For low cost high volume I would look at more diverse suppliers (China etc), for high cost/reliability known manufacturers (Molex, Amp, Samtec AB Connectors etc). Looking for a new flexi to PCBB connector set I spent two weeks just looking at what is out there these days!

Good luck, as headphones are a priime example of the weakest link, the smaller ones get so much abuse that they generaly break at some point, so they are for such a simple thing a challenge to design.

Have Fun
Marc

You have had a great deal of excellent information here. I would go and talk to a production engineer and see what he has to say about the relative merits of each method (costs v rejects v special machines. . .) before you finally select your course of action.
Frank

Like others are saying, you don't ever want to rely on a solder joint for mechanical strength if you can help it. That said, soldering directly to the board via a plated hole is still a reasonable connection, especially if labor cost isn't a big consideration. We use this method on a regular basis where cost is critical but labor is cheap.

If you do that, you'll need to minimize any relative motion between the wire and the solder point using other methods. Reinforcing the solder joints with epoxy or hot glue makes the assembly more robust with regard to handling. If you don't do that, you'll break wires off during testing and development just from handling the boards. Regardless of whether you do that, you'll need to build some strain relief into the next level of assembly between the wire and your enclosure. I've seen some good recommendations for ways to do that already. Over-molds are common and so is routing the wire through a "torturous path."

If you manipulate the wire outside of your enclosure and the wire-end on the inside also moves, even a little bit, then you don't have an effective strain relief. Even tiny movements repeated enough can break your solder connections.

Good luck!