Solder Mask is a protective coating applied to the bare printed circuit board. Bare boards are covered with mask to prevent accidental solder bridging during assembly and to help protect the board from the environment. This article will introduce 10 characteristics of PCB soldermask ink.
10 characteristics of PCB soldermask ink
Viscosity is short for dynamic viscosity. It equals shear stress / velocity gradient. Its international unit is Pa / sec (Pa.S) or mPa / sec (mPa.S). In PCB production it means the fluidity of ink driven by external forces.
Plasticity means after the deformation driven by external forces, the ink could still remain the properties as before. Ink plasticity will help improve the printing precision.
Thixotropic, also known as rock degeneration, sag resistance, is a physical characteristic of liquid. Its viscosity declines under stirring, but it will recovery its original viscosity at standstill very fast. By stirring, the thixotropic effect lasts for such a long time that the ink could re-constitute the internal structure. The soldermask ink becomes liquid when it is stirred. This accelerates the speed of ink through the screen mesh, and promotes the ink evenly fused.
Leveling is the ink expansion degree to the surrounding driven by external force. Fluidity is the reciprocal of viscosity. Fluidity is related with ink plasticity and thixotropic. Big plasticity and thixotropic, big fluidity.
Viscoelastic refers to the ink squeegee blade after being shear fracture ink quickly rebound performance. Requirements deformation speed ink, the ink can rebound quickly in favor of printing.
The slower the ink gets dried on the screen, the better. But the faster the ink gets dried, the better, when the solder mask is transferred to the substrate.
Fineness is the size of Pigment and solid particle. PCB ink size is generally less than 10μm, the fineness should be less than one-third of the mesh opening.
When the ink is stirred by the ink shovel, filamentous ink will be not torn, called stringiness.
Transparency and Opacity
For PCB ink, according to different usage, different requirements for transparency and opacity of inks are needed. In general, circuit ink, conductive ink and legend ink require high hi opacity. The solder resist is more flexible.
Safe and Environment-friendly
PCB ink requires low-toxic, odorless, safe and environment-friendly.
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