Genny,
Sounds like the problem may lie in the nature of Teflon(r) insulation. With PVC or related cousins, the insulation is compliant enough to distribute bending and shock over a the area of the bend and beyond; Teflon is not so forgiving, especially at low temperatures, even though it sounds like temperature is not a problem. This seems reasonable since the former cable was not causing such problems.
Molex makes a cable holder for 1.5mm, 2.0mm, and 2.5mm center ribbon cables in straight-in and right angle flavors. This device moves the point of stress up from the board to the end of the cable holder, away from the solder joint. Maybe something like this would help. A snug fit between cable and cable holder would be best to truly lessen the amount of strain at the solder joint, and you may have to glue (uggghh!) the cable holder to the board if it does not have any board retainers.
Just one of many ideas coming henceforth and forthwith.
Best Rgds,
Roger M. Stoops, CID
Trimble Navigation Ltd., Dayton, OH, USA
-----Original Message-----
From: Genny Gibbard [mailto:[log in to unmask]]
Sent: Friday, April 11, 2003 1:21 PM
To: [log in to unmask]
Subject: [TN] wire assembly suggestions
We have a midplane made of four interconnecting boards, involving time consuming detailed hand assembly to put together. Part of the interface of this board to other parts of the system is a terminal housing of 12 wires, 7 going to one midplane board and 5 going to another. The wires are about 2" long, soldered on the PCB end, crimp terminals on the housing end. Originally a 26 ga ribbon cable piece was used, but they wanted higher current carrying capability, so went to a 22ga ribbon cable. The ribbon cable is so stiff, that one prototype assembler suggested going to 24ga teflon coated stranded wire. The first few prototypes went fine and have exhibited no problems, but then it moved into production to finish off the proto build and give them experience with the assembly. Now it seems like on every assembly they are complaining some of the wires from the terminal housing are breaking off at the PCB.
The terminal housing sits very close to the midplane assembly, once mounted in the chassis, and there is very little positional movement once it is installed in the product chassis. The wires are probably longer than we need, but you need some length to ease the handling of assembling this. The wires go in sort of a J shape, straight out of the terminal housing and then curving down or up and back to the vias on the PCB's.
They were shown how the wires were preformed and routed off the boards to the terminal housing to limit the wiggling and strain they would go thru once they were soldered to the boards, and they say they've done that, but that they are still breaking. They INSIST we find another solution.
Suggestions?
Genny Gibbard ( mailto:[log in to unmask])
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