The graphics and text on PCB a circuit board is usually printed with a permanent non-conductive epoxy ink. The color is typically WHITE, although other colors may be available. Requirements are addressed in IPC-4781 QUALIFICATION AND PERFORMANCE SPECIFICATION OF PERMANENT, SEMI-PERMANENT AND TEMPORARY LEGEND AND/OR MARKING INKS.
I've never heard of a problem with Silkscreen as a material, except maybe some discoloration after high PCB reflow temperatures for RoHS compliant soldering. Silkscreen problems are almost always caused by circuit board DESIGNERS, so I'm going to take this opportunity to mention a few guidelines (which I will probably repeat in a later section, but worth repeating because designers often do not give silkscreen the attention it deserves!)
If silkscreen epoxy is printed over lands PCB or pads that will be soldered, it will melt into the solder joint during reflow and weaken the attachment. Therefore, silkscreen should always be printed on top of the mask material and never over solderable surfaces. Many CAD systems can clip the silkscreen away from exposed metal, but when creating library components be sure to keep the component outlines and polarity marks away from the pins (0.25mm) by default, and pay attention when moving or rotating reference designators or when adding text to PCB the final board design.
The width of silkscreen graphics can also be a problem. If too thin, PCB the fabricator will have problems in the screening or printing process and skips can occur. If too thick, the text may be too blurry to read. As components get smaller in size and circuit density continues to increase, it is sometimes very difficult to print silkscreen at all, but try to use line widths not less than 0.15 mm (6 mils), 0.18 mm to 0.20 mm is preferred PCB.
Solder pads should never be overprinted, because this may lead to problems during soldering, assembly, and with the E-Test. If we should detect an overprinted solder pad (spacing < 150μm), then Multi-CB reserves the right to remove the marking print at this location. Relevant for the definition of the solder pads is the solder pad exemption. The marking print is usually automatically clipped with a spacing of 100μm to the solder-stop edge.
|Silk screen printing method|
|productivity||For high / mass production|
|Coating thickness||It is relatively thick, but it gets scattered|
|Silk color||White, black, yellow|
It is a printing method using a plate material with chemical fibers in a mesh form. By rubbing ink with a squeegee, ink is pushed out between the meshes and printed on the board. For silk printing of printed circuit boards, it is a general construction method.
|Coating thickness||Thin but constant in thickness|
|Silk color||White / Black|
This is a method of applying ink to the entire surface of the substrate and then removing unnecessary portions. It is also suitable for printing fine patterns and fine designs because the resolution method is good and the finish is beautiful by the method used also in the pattern and resist process.
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