The difference between through hole cover oil and through hole opening window

The difference between through hole cover oil and through hole opening window

Regarding the options of Via window opening and Via hole cover oil, as well as the application distinction between PAD and VIA, many customers and design engineers often have questions when submitting PCB orders. They are confused about which option to select in the ordering system. ONESEINE TECHNOLOGY CO.LTD would like to give a detailed explanation of this common PCB engineering issue.

In daily PCB production, we frequently encounter issues caused by non-standard design files. Some designers do not clearly distinguish the definition of pads and vias. Conductive holes are sometimes defined with pad attributes, while keyholes are set as via attributes. Such mixed use of VIA and PAD attributes often leads to manufacturing errors and customer complaints.

From the perspective of PCB fabricators, CAM engineers may make processing mistakes when handling non-standard Gerber or design files. In some cases, experienced engineers will manually adjust customer files to fix non-standard designs and deliver acceptable boards. However, this practice is not encouraged. Relying on manual file correction makes designers overlook design flaws, which perpetuates non-standard PCB design habits.

It is important to note that a successful production in one project does not mean the original design file is correct. All PCB design and CAM engineers should strictly follow industry design standards. At ONESEINE TECHNOLOGY CO.LTD, our CAM team keeps customer file features as much as possible and processes PCBs strictly in accordance with design specifications. Any abnormal design issues will be fed back to customers promptly. This helps PCB designers optimize their design quality and reduce production disputes.

This article focuses on explaining the definitions of conductive holes, keyholes, as well as related settings in Protel, PADS and Gerber files. Mixed definitions of conductive holes, via keyholes and pads are the source of most manufacturing disputes, and typical problems are summarized below:

Errors during via conversion due to non-standard design or unfamiliar Gerber export rules

When customers submit Gerber files, PCB manufacturers cannot automatically distinguish vias from keyholes. The production will follow the graphic information in the Gerber data directly. If soldermask layer graphics exist on the hole area, the factory will open a window on the via; if there is no soldermask opening on the layer, the via will be covered by solder mask.

Common dispute scenario: Customers expect via holes to be covered with oil, but the final boards come with via windows. Exposed copper on vias may lead to short circuit risk. In such cases, the Gerber file must be reviewed first. Gerber is a photoplot file, the factory cannot judge whether a hole is a conductive via or a keyhole, and the soldermask layer determines whether the hole is tented or opened.

Mixed definition of pad and via resulting in processing errors

If you submit Protel or PADS design files and require via hole cover oil, double-check whether your plug holes are defined as vias. If plug holes are set as vias, these holes will also be covered by green oil, and components cannot be soldered onto the pads.

Common dispute scenario: Through-hole plug-in pads require tin exposure for soldering, but the pads are covered with solder mask. We need to verify if the hole is defined as pad or via in the original design.

Another frequent case: Customers submit Protel/PADS files and select through hole cover oil on the order. But conductive holes are drawn using pad definitions instead of vias. The pads will be opened by default, which conflicts with the requirement of via tenting. The dispute usually arises: "I want conductive holes to be covered with oil, why are the holes opened?" Again, the root cause lies in non-standard file definition.

ONESEINE TECHNOLOGY CO.LTD hereby clarifies our processing rule: features defined as via will be processed as vias, and features defined as pad will be processed as pads. There is no other way for the factory to tell conductive vias apart from plug-in holes. VIA and PAD attributes are the only identification standard for PCB manufacturing. Please keep this rule in mind for your PCB design.

How to set via hole cover oil in Protel and PADS

Protel has a tenting checkbox in the via property menu. If the tenting option is ticked, vias will be covered with solder mask, and the exported Gerber files retain the tenting setting.

For PADS software: When exporting soldermask layers, if you check the option of solder mask top - via underneath, all vias will be opened. Leave this option unchecked if you need vias to be covered with solder mask.

To sum up: PAD is inherently the attribute for plug-in holes. VIA supports two soldermask treatments: tenting (cover oil) and window opening. If you supply original design files, you can select the via processing option when placing orders. If you only provide Gerber files, carefully verify the soldermask layer graphics to ensure they match your requirements.

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