Why printed circuit board manufacturers use plated slots ?

Printed Circuit Board Plated Slots

Slots are holes, which are either plated or non- plated-through. So, plated slots are holes plated in copper. And we use them for electrical connections on the PCB. A through slot is the one that goes to the entire depth of the board, starting from one end to another. Whereas a PCB outline or edge also has plating called side plating.

printed circuit board manufacturers use plated slots for components packaging, however, non-plated slots are also in practice. But, PCB with multiple layers have only plated-through slots.

Why Prefer Plated Slots?

PCB assembly involves different designs and components, and you would often see round holes to accommodate the round components or square as well. A round hole suits a PCB with through-holes. However, certain components are compatible with the blade or rectangular leads, so the round or square holes are not ideal in that case, and this is where a plated slot works.

When the pin size becomes large, the rectangular connectors work with plated-through slots rather than round holes. Like, they are ideal for the DC Jacks. Though you can use the round holes for small connectors and rectangular pins, plated slots are better because they take less space on the PCB, unlike the round holes.

Difference between Plated And Non-Plated Slots

Plated slots have copper plating in the circuit layer, whereas it opens in the solder mask.
On the other hand, non-plated slots don’t have copper plating in the circuit layer, besides, it does not open in the solder mask.

Design of Plated Slots

There is a specific way to show plated holes on the Gerber, like:

• You have to put the copper pads on the upper and lower solder mask.
• Then you insert a milling slot in the mechanical layer.

Designers prefer a mechanical layer to put slots in the Gerber and it involves two possible options to do it.;

Use of Flashes Having the Right Size Slot

Drawing a slot with a 0.50 mm thick line, as it helps designers to check it visually to ensure that there is enough tolerance between copper and the PCB edge. Remember that a line’s center is considered the edge of the slot.

Then you have to join the slots with the PCB outline into the Gerber, and it should be parallel to the copper layer. However, the copper layer should also have a PC Board outline to stay on the safer side.
The mechanical layer in this case has different names, depending on the system. It also depends on milling as it should be there. However, you can use another layer in the absence of a mechanical layer. Use the README file to avoid any doubts regarding the right file.

Don’t always define slots in a legend or a copper layer because they could be misinterpreted. Show large slots in the legend or copper layer, however, the outline should be precise. Don’t forget to write the text SLOT in the center.

Creating a Drill File

You can also define the plated slots through drill files as it is a precise way, however not all CAD software allows this option. But, defining through the drill files involves the X and Y or the slot width and length, instead of a complete row of holes that overlap.

Understanding A Small Slot In The PCB

The size of the smallest slot varies, depending on the type of the PCB, like if it’s flex, rigid, or rigid-flex. The width of the smallest slot is 0.50 mm for a rigid and flex-rigid PCB, and the length is often 1.0 mm.

These sizes are so due to more thickness of the PCB, besides, the slots are created through the NC milling that is mechanical. As, the grooving cutter of NC is 0.50 mm and its length is twice the width, like 1.0 mm.

On the other hand, the thickness of the flex PCB is less, and you can make slots through a laser machine. Designers prefer the smallest slot because the bigger slot’s length becomes more which is twice its width.

Milling Of the Cutouts Or Slots

You have to use the round NC grooving bit for the milling of slots in the rigid PCB, and it’s just like the CNC machine. However, the inner corners of the slots are made round instead of sharp. Whereas the PCB edge is created to the center of the border.

Which Industries Can Use the Plated Slots?

Mostly the thick or multilayer PCBs have plated slots, and such boards are ideal for different industries, including aerospace, consumer electronics, computer, and telecommunications. As these slots don’t take much space, they are cost-effective in terms of making. A board with both plated slots and round slots is also ideal for multiple electrical connections.

Frequently Asked Questions

What Is A PCB?

PCB stands for a printed circuit board having different electrical components, holes, and other features. Various industries use PCB boards to provide the electrical signals to run different devices or electronics. A PCB board can be embedded, single or double-layered, or can have many layers like up to 60 plus.

What Is The Definition Of A Plated Slot?

A plated slot is a hole in the PCB with copper plating. It is not round, so it is ideal to accommodate the leads with rectangular pins. You can use such a slot for electrical connections and component packaging
The slot goes throughout the circuit board that’s why we call it a plated-through slot.

What Is Edge Plating?

If plating is done on the edges of a PCB, we call it edge plating. Besides, you can also call it the side plating of a circuit board. It goes from the upper layer to the lower layer of the PCB, extending to an edge of the perimeter.

Which Circuit Board Should Have Plated Slots?

Generally, the multilayered PCBs have slots with plating also known as plated-through slots. However, there are also non-plated slots, depending on the PCB design and its application.

Do I Need A Lot Of Space For Plated-Through Slots?

Plated slots are mostly rectangular, hence they don’t take much space on the PCB like the round slots. So, such slots are ideal when you run short of space on the PCB, and where you need to use the rectangular Jacks.

What is a Copper Layer?

PCB has different layers of which one is a lamination made of copper foil, and it is attached to the circuit board with some adhesive. The copper layer is essential for a two-sided PCB, including copper on both sides. But, PCB boards with more than 60 layers of copper are available by different companies.

What is Solder Mask Layer?

The green color on the circuit board is a solder mask and its surface is called the solder mask layer. The purpose of the solder mask is to cover the exposed copper to prevent users from the electric shock upon contact. Though it is mostly green, other colors are also available.

Final Thoughts

PCB manufacturers use plate slots for components packaging, however, the non-plated slots are also in practice. But, PCB with multiple layers has only the plated-through slots. Certain components are compatible with the blade or rectangular leads, so the round or square holes are not ideal in that case. This is where a plated slot works.

Plated slots have copper plating in the circuit layer, whereas it opens in the solder mask. Non-plated slots don’t have copper plating in the circuit layer, besides it does not open in the solder mask.

The size of the smallest slot varies, depending on the type of PCB, like if it’s flex, rigid, or rigid-flex. The width of the smallest slot is 0.50mm for rigid and rigid-flex PCB and the length is often 1.0 mm. Engineers use cad software to make Gerber files for different types of slots including plated through and non-plated through slots.

Would like to know best practices for Plates Slots or printed circuit board assembly? Email us at sales@pnconline.com

Written by Sam Sangani

Sam Sangani is the President & CEO of PNC Inc., a Nutley, NJ based Printed Circuit Board manufacturer. Sam graduated from L. D. Engineering College with a BS Degree in Mechanical Engineering. He also continued his education and graduated from Steven’s Institute of Technology where he acquired a Master’s degree in Computer Science.

After completion of his BS, Sam worked as a QC Manager, for Xerox, Romania and London. He was responsible for the Quality Control of Cable and Wire Harness imports from Romania. After completing his Master’s Degree, he worked as a Senior Programmer with IBM, Tucson, Arizona. Sam was responsible for leading the Mainframe System Programming Team.

In 1997, Sam acquired PNC INC., a Nutley, NJ based PC Board fabrication Shop. From 1997-2013, Sam has made tremendous improvements and changes within PNC INC., as he added many new Products and Technologies in PNC’s portfolio. With his proven track record and leadership, PNC has never had an unprofitable year and has continued its growth yearly since 1997.

His current responsibilities are Strategic Planning, Corporate Management, New Business Ventures, Sales & Marketing, Trade Shows, Professional Services and leading productive teams to achieve peak potential. He has also utilized Lean Management techniques which have built a foundation for PNC’s high-paced growth. Sam also enjoys real-estate investing, web design & SEO, trading stocks, options, futures and Forex markets.