Custom PCB Board Assembly Soldermask
The color that most people are familiar with when it comes to motherboards is green, the color of soldermask. Though not nearly as common, soldermask also sometimes appears in other colors, such as red or blue. Soldermask is also known by the acronym LPISM, which stands for liquid photo imageable soldermask. The purpose of soldermask is to prevent the leakage of liquid solder. In recent years, incidences of this have become more common due to a lack of soldermask. By most accounts, however, users generally prefer boards that have soldermask over boards that don't.
Once soldermask has been applied to PCB, the PCB is subjected to molten solder. As this process occurs, exposed surfaces of copper become solderized. The whole process is known as hot air solder leveling (HASL). As SMD chips are soldered, the board is heated to the point where solder takes on a molten form and the components are put into their proper place. As the solder dries, components also become soldered. HASL usually includes lead as one of the compounds in the solder, though lead-free options also exist.
The spacing of track width is indicated by a dash. For instance, when you see the figure 6/6 mils, that would specify 6 mils as the minimum track width, as well as the minimum track spacing. Therefore, all spacings on the board in question should either meet or exceed 6 mils. For those unfamiliar, mils units are used to determine distances on PCB materials. Width and spacing are especially important when it comes to boards that are designed to handle high amounts of current.
When a custom PCB board assembly is multilayered, various tracks cannot be examined visually for their accessibility. Therefore, a test is performed that places probes at the end of tracks to verify all of the signals are reachable. The test is carried out with applications of volts from one end. If these voltages are sensed from the other side, the tracks are deemed to be in working condition. While the test is not always essential on boards with only one or two layers, it's still recommended if you truly care about quality.
Vias that connect inner and outer layers are known as blind vias. The name is results from the fact that because such vias can only be spotted from one side. Vias that connect two or more inner layers are known as buried vias, which cannot be spotted from the outside on either side. On boards that contain blind and buried vias, via filling is often used. This keeps the outside surface more secure and helps lower the possibility of solder slipping through and penetrating the inner vias.