PCB Surface

PCB surface finish include: PCB plating finishes is a coating between a component and a bare board PCB. It is applied for two basic reasons: to ensure solderability, and to protect exposed copper circuitry. As there are many types of surface finishes, selecting the right one is no easy task, especially as surface mounts have become more complex and regulations such as RoHS and WEEE have changed industry standards.

Recently, the common surface PCB treatment technologies which GreensTone may use when manufacturing PCBs are HASL(hot air solder leveling), organic coating (OSP), electroless nickel/gold, immersion silver, immersion gold, etc.

The solder mask is mainly Liquid UV Photo-imageable Ink with green, red, black, yellow, white, matt black/green, bule, gray, etc. green should be the most commonly used one. The suggested soldermask clearance in GERBER is 2-4 mils.

The silkscreen layer is the top layer of the PCB and serves as a reference indicator for placing components on the PCB. The graphics and text on PCB, a circuit board is usually printed with a permanent non-conductive epoxy ink. The color is typically white. Screen printing is used to specify useful information on the PCB board, which can help users during the assembly. It is used to mark component values, part numbers, test points, polarity, etc.

PCB Surface Features

PCB surface finish Comparison of cost and solderability

Actual solderability: Electroplating nickel gold> HASL > OSP > ENIG >Immersion silver >Immersion tin

Cost: Electroplating nickel gold > ENIG > Immersion silver> Immersion tin > HASL > OSP.

The functions of the solder mask layer on the PCB board

Preventing short circuit from bridge connection in the soldering process

Preventing the physical breakage of a conductor circuit

Prevent short circuit between conductive lines and solder joints when proceeding reflow soldering, wave soldering, and manual welding

Preventing the copper layer from oxidation

Its high Insulating brings the possibility to the high density of PCB finish

Here are three main ways to add silkscreen coating on a PCB

Manual screen-printing: This is a process that can be used when line widths are greater than 7 mm and the registration tolerance is 5 mm.

Liquid Photo Imaging (LPI): This process provides more accuracy and legibility over manual screening and is used when line widths are greater than 4 mm

Direct Legend Printing (DLP): This is the most accurate way of adding a silkscreen, however, it is very expensive.

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