From: "Mike Hatch" <mike at
brickfieldspark.org>
I haven't
heard anyone discuss this yet: what causes traces on some old
PCBs to wrinkle and not others? My guess is a combination of suboptimal
glue and wide temperature swings.
Caused by the hot air solder levelling process when a manufacturer skips a
process or has the process order slightly out.
The solder should only be deposited on the component pads, but some
manufacturers used to put the solder on before the silk screen, then level
the board. The solder melts during levelling and aggregates under the mask
forming the "wrinkles".
It should be - silk screen, apply tin/lead to pads, level.
It can be - tin/lead, silk screen, mask, level.
but if its - apply tin/lead, silk screen, level - you get wrinkles.
You seem to be implying that the wrinkles are a result of the PCB manufacturing
process, and that is wrong; the wrinkles you are talking about occur during wave
soldering at the assembly portion of the process. By going to SMOBC (Solder Mask
Over Bare Copper), both the wrinkles and extra weight of solder picked up during
the wave soldering process were eliminated. And of course, it was not a problem
when the boards were hand soldered.
The wrinkles are NOT caused by hot air leveling (that was my area of expertise
when I was working as a field engineer installing/training/maintaining Gyrex Hot
Air Levelers.) I know of no process or reason for putting soldermask over
tin/lead and using Hot Air Leveling for the reflow process. Hot air leveling was
mainly used for SMOBC boards. Solder gives a longer shelf life than the
SealBrite coatings that were also fairly common a number of years ago, and thus
Hot Air Leveling was also used on some boards without soldermask.
The usual manufacturing process before hot air leveling was drill, electroless
copper/copper plate, plating resist applied (either photographically or
silkscreening), copper plate to desired thickness, tin/lead plate, strip resist,
and etch. If the board was going to be hot air leveled, the tin/lead plating was
chemically removed. Otherwise it went through a reflow process to alloy the
tin/lead into solder before the soldermask was applied.