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Not really a question but an observation. Was zipping across evilBay earlier today and came across this slightly used avionics chassis putatively from a Russian SU-34 shot down over Ukraine.
There's nothing surprising at first glance. You can see a light alloy casting, in which are inset several light alloy stampings. The individual Circuit Card Assembly (CCA) connecters are attached to the stamped metal tray. There do not appear to be any supprts for the CCAs (such as Birtcher guides). There is also no motherboard - that must be on the other side.
But wait, the bottom view shows no motherboard at all, but that each pin on each CCA connector has been placed, wire-wrapped, and soldered by hand! The cost in touch labor and Quality Assurance checkout and correction hours (not money) must be astronomical. Western practice would be to hand-stuff the Printed Circuit motherboard with the connectors and then pass the assembly through a wave-solder machine (much as is done on commercial computer mother/logic boards).
I would assume that the producability people at the Russian [factory of origin] made a decision not to spend the rubles on the non-recurring engineering necessary to create a 15 to 20 layer printed wire board and just incur the touch labor cost when building at low-rate production (15-25 LRU end items/year - assuming the LRU is unique to what is identified as the "SU-34"). The other conclusion could be that the technology to design/ build multi-layer boards was not available or economical for the particular application.
To have wire-wrap in flying avionics is quite different that Western practice - usually wire-wrap is seen only as far as the brassboard prototype stage or in bespoke/prototype flight test assets; not a frontline combat aircraft.
Thoughts from the commentertiat?
There's nothing surprising at first glance. You can see a light alloy casting, in which are inset several light alloy stampings. The individual Circuit Card Assembly (CCA) connecters are attached to the stamped metal tray. There do not appear to be any supprts for the CCAs (such as Birtcher guides). There is also no motherboard - that must be on the other side.
But wait, the bottom view shows no motherboard at all, but that each pin on each CCA connector has been placed, wire-wrapped, and soldered by hand! The cost in touch labor and Quality Assurance checkout and correction hours (not money) must be astronomical. Western practice would be to hand-stuff the Printed Circuit motherboard with the connectors and then pass the assembly through a wave-solder machine (much as is done on commercial computer mother/logic boards).
I would assume that the producability people at the Russian [factory of origin] made a decision not to spend the rubles on the non-recurring engineering necessary to create a 15 to 20 layer printed wire board and just incur the touch labor cost when building at low-rate production (15-25 LRU end items/year - assuming the LRU is unique to what is identified as the "SU-34"). The other conclusion could be that the technology to design/ build multi-layer boards was not available or economical for the particular application.
To have wire-wrap in flying avionics is quite different that Western practice - usually wire-wrap is seen only as far as the brassboard prototype stage or in bespoke/prototype flight test assets; not a frontline combat aircraft.
Thoughts from the commentertiat?
