Arjen, For insulation over PCB traces, some types of dry film solder mask might be suitable. These films are manufactured to a consistent thickness, and then laminated to the PCB. You need to check with your board vendor as to types and approval ratings. These films are very tough, just ask anyone who has ever tried to scrape through one in order to expose a trace for rework.
You will want to make sure that your PCBs are fabricated as SMOBC, or solder mask over bare copper.Tin coatings have a tendency to flow when boards are wave soldered or reflowed, and may weaken the integrity of solder mask. You will also get better performance at high frequencies. As to conformal coatings, there are several issues to consider. The first is cleanliness. No-clean flux leaves a thin film over the PCB surface which will prevent proper adhesion of coatings. Most conformal coatings are intended for protection against moisture and humidity, and voids under the coating won't matter. For arc prevention, the coating must adhere tightly to the board and components. The second issue is how much of the board to coat. Coatings tend to interfere with repairs. Even "repairable" coatings make the job more difficult, and more importantly, tend to create voids when heated with a soldering iron. If only certain portions of your boards require protection you might consider selectively applying an epoxy potting compound to those areas. I hope that this will be of some help. Scott --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
