A broken circuit board, depending on the break, where and how it is broken, often renders it scrap as it would require the skill of a surgeon to effect a repair with delicate tools such as a surgeon might wield. This is doubly so in the case of a double-sided circuit board...
A cracked circuit board on the other hand, where only a few tracks are broken, is a different matter. The crack can be realigned and stabilised with Superglue, the varnish carefully scraped from the damaged tracks either side of the crack for a quarter inch and then a suitable strand of solid copper wire soldered in to bridge the break.

Where a track is impossibly narrow, it is possible to solder in a short jumper wire from a suitable point to another convenient point, ensuring at all times to use as little heat as possible.

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