I'm sure this isn't true of PC motherboards etc.
What do you mean??
It is many years since any computer motherboard used edge connectors
so how does this apply to PC's which never used them?
The ones used for DIMM SIMM etc at least have a locking mechanism. There are
issues wrt whether the contacts are tin or gold plated though.
What makes edge connectors more expensive (whether tin or gold plated)
is the fact that the edge connector must be formed as part of the pcb
manufacturing process. Once etched, the edge connector part is then
electrolytically plated and the commoning strip used to connect the
pads (for electroplating) is then trimmed off during drilling and
routing and then chamfered. The board handling and processing is thus
made so much more expensive compared to using modern two part
connectors. That's the main reason this process isn't used today,
except in certain circumstances. It was not so much a question of
reliability because they were at least as reliable as two part
connectors.
I have found the variation in pin dimensions and receptacle tensioning
on some very reputable two part connectors to be quite variable such
that the reliability from batch to batch was quite poor. At least with
pcb card edge connectors the board and copper thickness was fairly
standard and only the socket manufacturing could be variable thus
reducing the probability of poor reliability of connection due to
manufacturing defects and errors by 50%.
Ross H