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Ultimate Guide of PCB Solder Mask Opening Updated in 2022

PCBONLINE Team

Wed, Mar 16, 2022

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Solder mask opening is a common PCB design and manufacturing requirement. This post from the PCB manufacturer PCBONLINE reveals solder mask opening from the below content:

Part1: What is PCB Solder Mask Opening

Solder mask is a PCB oil layer that covers the copper wires and PCB materials to insulate and protect the PCB external from shorts and the environments. On the solder mask layer, you need to create openings to allow PCB pads to solder or connect, and some vias without PCB ink covered for thermal dissipation. These openings on the solder mask layer are called solder mask openings.

solder mask opening for PCB vias

During PCB design, you should take note that the solder mask is those empty zones. When it comes to PCB manufacturing, those empty zones are printed with PCB ink in green, black, white, or another color. Instead, the shapes on the solder mask layer in your PCB design are solder mask openings, where the copper is exposed.

Part 2: When Do You Create Solder Mask Opening

Solder mask opening is required for the below four situations.

Solder mask opening for PCB pads

PCB pads are the contacts that need to be surface mounted with electronic components, such as resistors, capacitors, ICs, etc. So PCB pads should not be printed with PCB ink. That means when you do the PCB design, in the solder mask layer, you should create a solder mask opening for each PCB pad.

Solder mask opening for PCB Vias

Not all PCB vias need solder mask opening, it all depends on your PCB needs.

For better thermal dissipation of your PCB, you can design solder mask openings for the PCB vias. Especially for power supply PCBs that flow large currents, solder mask opening for thermal dissipation is common. You can also fill in the solder mask opening with tin, which acts as a metal heat sink.

Solder mask opening for PCB vias also serves as a PCB test point. Because the copper is exposed, you can process PCB tests here.

Above are two purposes of solder mask opening for PCB vias. However, PCB vias can also be prayed with solder masks to protect the copper from oxidation, especially from aggressive environments.

Solder mask opening for gold fingers

solder mask opening for gold fingers

PCB gold fingers are a column of exposed hard gold plating pads on the PCB edge for plug-in and connection. Solder mask opening is necessary for gold fingers because solder mask is insulative while gold fingers serve for connection and need to have excellent conductivity.

You don't need to worry about the oxidation of the gold fingers without solder masks. The surface finish, hard gold plating well protects the copper pads.

Solder mask opening for ground

You can design solder mask openings for PCB grounding. The exposed copper can connect with the metal shell. In this way, the PCB is grounded.

Solder mask opening for copper thickness measurement

During PCB manufacturing, we need to measure the PCB copper thickness to see if it is qualified. So PCBONLINE sometimes may suggest solder mask opening to you depending on your specific project.

Solder mask opening for PCB antenna

PCB antennas transmit and receive RF microwaves and will consume much power. For high-frequency PCBs, solder mask opening for PCB antennas is common, because the antenna can consume smaller power.

Part 3: What is the Size of Solder Mask Opening

During PCB manufacturing, the solder mask opening size should be larger than the pads or copper areas desired to be exposed. Because of the skin effect, the PCB oil around the solder mask opening will gather, and the exposed area will be smaller. Usually, the width/length of the solder mask opening is 4mil larger than the pads.

Do you need to set up the solder mask opening size during PCB design? No, you don't have to. You just need to keep the same size as the required exposed pad/via size because the EDA tool will automatically enlarge the solder mask opening size.

What's more, when you deliver your Gerber/IPC-2581 to the manufacturer PCBONLINE, we will check the solder mask opening size in design for manufacturing (DFM) before production. If there's any issue, we will assist you to modify it until everything is correct.

Solder Mask Opening and One-Stop PCB Manufacturing Without Hassles

PCBONLINE is an advanced PCB manufacturer that has rich design and fabrication experiences in solder mask opening. Founded in 1999, we have two large PCB manufacturing bases and one PCB assembly factory.

PCB manufacturer PCBONLINE

Here are reasons for you to consider PCBONLINE as your PCB supplier:

    • We provide free DFM, DFT, DFX to make sure the solder mask opening size is appropriate.
    • Our professional engineers will assist you in solder mask opening throughout your project.
    • ISO, IPC, IATF 16949, UL, REACH, ROHS-certified PCB/PCBA quality management.
    • From prototypes to batch production, PCB design, manufacturing, assembly, tests, can be done one-stop from PCBNLINE.
    • Our PCB manufacturing factory in Jiangsu can process PCB gold finger hard gold plating.

If you have PCB manufacturing needs or have concerns about solder mask opening in your project, please feel free to send your inquiry or questions to PCBONLINE by email at info@pcbonline.com.

Conclusion

Solder mask openings are the shapes designed on the solder mask layer. On the PCB, solder mask opening allows PCB pads to solder, gold fingers to connect, exposed vias or copper areas for thermal expansion, grounding, etc. If you want assistance in solder mask opening for your project or if you want PCB/PCBA manufacturing, don't miss the 23-year-old source factory PCBONLINE.


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