PCB soldermask process and some bad issues

Soldermask is printed on the surface of the PCB with a layer of ink, which plays an insulating role, but also a role in protecting the copper surface, playing a role in beautiful and beautiful, it is like wearing a piece of clothing on the outside of the PCB, so it’s extremely easy to find any defects are very easy to find, so the soldermask is the most likely to incur the most customer complaints of all the processes in the process. solder mask sliver

What is a solder mask?
A Soldermask bridge is a component pad of an open window to another open window between the green oil the soldermask bridge, generally refers to the more dense IC pins corresponding to the IC pads between the soldermask. The role of the solder resist bridge is to prevent the flow of solder when welding, to prevent the device even in short circuits. Usually to prevent the welding of even tin short circuits, are to ensure that the pads of the soldermask bridge. solder mask sliver

Solder Resistance Design in PCB Processing
The minimum solder mask gap, minimum solder mask bridge width, and minimum N-cap extension size depend on the method of transferring the solder mask pattern, the surface treatment process, and the copper thickness. Therefore, if a more precise solder mask design is required, it is necessary to check with the PCB board manufacturer.
(1) 1OZ copper thickness conditions, solder mask gap greater than or equal to 0.08mm (3 mil).
(2) 1OZ copper thickness conditions, solder resist bridge width greater than or equal to 0.10mm (4mil). As a result of sinking tin (lm-Sn) potion on the part of the solder resist has an attack, the use of sinking tin surface treatment when the solder resist bridge width needs to be increased moderately, generally a minimum of 0.125mm (5mil).
(3) 1OZ copper thickness conditions, the conductor Tm covers the minimum extension size greater than or equal to 0.08mm (3 mil). solder mask sliver

Soldermask design of the conductor hole is an important part of the design of PCBA processing manufacturability. Whether or not to plug the hole depends on the process path, and guide hole layout.
(1) through-hole solder mask has three main ways: plug holes (including half plug, full plug), open a small window, and open a full window.
(2)Soldermask design for BGA via holes

Some common PCB solder mask problem and its improvement measures
Problem: Penetration, blurring
Reason 1: Ink viscosity is too low.
Measure 1: Increase the concentration without adding thinner.

Reason 2: The distance between the stencil and the printing surface is too large or too small.
Measure 2: Adjust the spacing.

Problem: Ink not drying
Reason 1: Oven exhaust is not good
Measure1: Check oven exhaust condition

Reason 2: Insufficient oven temperature
Measure 2: Measure whether the actual temperature of the oven reaches the required temperature of the product.

Reason 3: Thinner is not enough.
Measure 3: Increase the thinner and dilute it sufficiently.

Reason 4: Thinner dries too slowly
Measure 4: Use matching thinner.

Problem: Green oil bridge broken
Reason 1: Insufficient exposure to energy
Measure 1: Increase exposure energy

Reason 2: The Board was not treated properly
Measure 2: Check treatment process
……solder mask sliver

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