Tom
10-25-2002, 02:55 PM
IPC Advanced Study Guide Page Reference: Page 29 Section 1.4
Solder mask is a polymer used to protect the printed board's surface conductors from moisture. Unlike laminate material, however, it is not a composite but a homogeneous material. As the name suggests, it is used to mask off the outer areas of the board where solder is not required and provides an excellent protective coating over fine conductors on the surface of the printed board. In addition to protection from mishandling, dust or dirt, dendritic growth and other contaminants are also kept away from the very fine conductor spacing.
There are two broad categories of solder mask. These are permanent and temporary. Temporary solder masks are washable or peelable. They are used during the wave soldering process to prevent filling of holes that must be kept open for the installation after soldering of such leaded items as unsealed parts that might not withstand the cleaning or soldering processes. The temporary mask can be peeled off after processing is complete. Temporary masks are also used to protect gold fingers, which must not be soldered.
Washable masks are more convenient than peelable masks because they come off in a cleaning operation after wave soldering and do not need an extra step to remove them. The aqueous washable masks require a water cleaning system and the solvent washable mask must be washed in a solvent cleaning system.
Permanent solder mask also comes in several configurations. First there is the dry film and wet film processable solder mask materials. As the name implies, the dry film mask is on a separate polymer film that is applied to the printed board by heat lamination. The dry film masks can be developed with the excess removed using either an aqueous or solvent based solution. Dry films usually require photo imaging to define the pattern.
Wet film solder masks are also, as the name implies, liquid and paste-like. They include photoimageable masks and wet screenable solder masks. The screenable solder mask is differentiated by the method of cure. Some wet, screenable solder masks can be cured by UV light and some can be cured thermally in convection or IR ovens. The UV masks do not provide as good an adhesion as thermal masks, but require only seconds to cure as opposed to a 30-60 minutes cure cycle. Some photoimageable solder masks utilize both UV and thermal curing.
Solder mask is a polymer used to protect the printed board's surface conductors from moisture. Unlike laminate material, however, it is not a composite but a homogeneous material. As the name suggests, it is used to mask off the outer areas of the board where solder is not required and provides an excellent protective coating over fine conductors on the surface of the printed board. In addition to protection from mishandling, dust or dirt, dendritic growth and other contaminants are also kept away from the very fine conductor spacing.
There are two broad categories of solder mask. These are permanent and temporary. Temporary solder masks are washable or peelable. They are used during the wave soldering process to prevent filling of holes that must be kept open for the installation after soldering of such leaded items as unsealed parts that might not withstand the cleaning or soldering processes. The temporary mask can be peeled off after processing is complete. Temporary masks are also used to protect gold fingers, which must not be soldered.
Washable masks are more convenient than peelable masks because they come off in a cleaning operation after wave soldering and do not need an extra step to remove them. The aqueous washable masks require a water cleaning system and the solvent washable mask must be washed in a solvent cleaning system.
Permanent solder mask also comes in several configurations. First there is the dry film and wet film processable solder mask materials. As the name implies, the dry film mask is on a separate polymer film that is applied to the printed board by heat lamination. The dry film masks can be developed with the excess removed using either an aqueous or solvent based solution. Dry films usually require photo imaging to define the pattern.
Wet film solder masks are also, as the name implies, liquid and paste-like. They include photoimageable masks and wet screenable solder masks. The screenable solder mask is differentiated by the method of cure. Some wet, screenable solder masks can be cured by UV light and some can be cured thermally in convection or IR ovens. The UV masks do not provide as good an adhesion as thermal masks, but require only seconds to cure as opposed to a 30-60 minutes cure cycle. Some photoimageable solder masks utilize both UV and thermal curing.