A frequent question that I see come up on vintage computer forums is whether wrinkled traces on a Commodore 64 motherboard cause problems. Not all boards have this so it’s easy to see why this could be concerning.
The wrinkled traces on old PCBs like Commodore 64 motherboards is an artifact of the manufacturing process. It’s normal and it rarely causes a problem.
Do wrinkled traces cause a problem?
Usually, the wrinkled traces on a Commodore 64 motherboard and other vintage PCBs aren’t a problem. In theory, if the wrinkling prevented a good connection it could be a problem, but as long as you can measure continuity on both sides of a suspect trace, there’s no problem. The boards were tested at the factory and bad ones got fixed, so when it was a problem, someone already found and fixed it.
But it’s usually excess solder that causes the wrinkles. And more metal improves conductivity rather than harming it, so that’s not a problem. It looks odd compared to modern boards with uniformly smooth traces, but part of the charm of retro computers is that they look different, right?
I think so at least. And in this case, it shows part of your motherboard’s manufacturing process had human beings involved, unlike later boards that are almost entirely made by machines. It’s one reason computers are so much cheaper today, because less labor goes into making them now. Ironically the thing that makes the board look more questionable also made it more expensive.
What caused the wrinkled traces on a Commodore 64 motherboard
Commodore used a process called HASL, for Hot Air Solder Leveling. This put a layer of tin on the traces before applying the solder mask. This helped avoid corrosion and made it easier to solder the components to the board when the time came.
When the tin went on smoothly, you got smooth, level traces. On boards where the tin didn’t go on completely smoothly, you got wrinkles, both from the tin and from the wave soldering process drawing excess solder down under the mask. This more frequently happens on the larger ground plane, but can happen on large traces as well.
I see wrinkled traces more frequently on early Commodore 64 motherboards than later boards. In 1983 and 1984, Commodore literally couldn’t build C-64s fast enough to keep up with demand, so it makes sense that their work would be a bit sloppy. After 1984, the C-64 continued to sell, but in smaller, more manageable quantities. At least in my experience, boards made after 1984 are less likely to have wrinkled traces on the underside. You can date a board by looking at the date codes on the chips, and also from the board revision. The date codes on Commodore chips tend to be all over the place, but usually the majority of the chips will be within a few weeks of each other. It’s not unusual to find a couple of chips that are way out of range, but those are usually chips that replaced original chips that failed.