In recent years, there has been a marked increase in the variety of small portable wireless electronic devices. This expansion does not encompass radios and even mobile phones, which have been with us for quite a while, but includes wearable medical devices, internet remote controls and other gadgets. The smallest of these devices are typically comprised of a single PCB or system on a chip (SoC) technology with wireless connectivity (if required). For PCB manufacturers, this is a welcome evolution, as these devices do not have PCB connectors.
Single board technology is great; however, most electronic systems contain multiple boards that require interconnectivity and therefore have PCB connectors. There are distinct signal integrity advantages to having multiple small boards instead of larger ones with multiple signal types. Additionally, multi-functionality is also a growing design paradigm for platforms, and wires and cables offer greater signal transmission flexibility. PCBs are manufactured in panels that must be separated into individual boards. Connectors can complicate the process, especially when board edge clearance is at a minimum or there is an overhang.
Let’s take a look at some common PCB connectors and discuss some panelization design guidelines to help mitigate any manufacturing issues they may cause.
Common PCB Connectors
Most electronics systems include multiple boards that exchange information and data via wire, cable or pin connection. Additionally, boards with active components, such as amplifiers and ICs, require external power supplied via a PCB connector unless onboard batteries are used. Connectors come in many sizes and shapes, may be keyed or unkeyed (to prevent incorrect cable usage), or may lock or latch. Manufacturers sometimes create custom connectors designed to work with their devices and boards; however, there are standard or common PCB connectors that are easy to replace and simplify the process of connecting systems from different manufacturers.
Common PCB connectors can be categorized into classes based on how the connection is made.
- Terminal blocks - May be on the PCB or separate from the board. These may accept different types of connections (e.g., direct wire, rings, forks).
- Binding posts - Typically accept stripped wires.
- Blade - Designed to accept a flat conductor.
- Ring - Connect onto a specific size post and usually held in place by a nut or bolt.
- Fork (or spade) - Similar to a ring, except the connector slides onto a conductor.
- Screw - Held in place by locking. Typically, for quick connect/disconnect. For example, a Bayonet Neill–Concelman or BNC connector.
- Plugs - A large class of fixed connectors that accept cables or wires. This includes headers, USB, HDMI and Ethernet.
- Sockets - Similar to a plug. Accepts connection from a movable conduit, cable or wire.
- Gold fingers - Etched connectors used for boards that will undergo repeated insertion and removal.
The list above is not exhaustive but does contain the most common PCB connectors. For connectors that mount on PCBs, the usual design restrictions, such as spacing, apply. However, location is the most important concern and it is generally preferable to place connectors on or near the edge of the board.
Guidelines for Designing Panels for Common PCB Connectors
PCB connectors are typically located around the edge of boards to avoid the physical contact of cables and wires with other components; minimize trace route lengths by having signal input/output (I/O) ports close to the components that use them; easily isolate different signal trace routes to minimize electromagnetic interference (EMI); provide greater flexibility over trace width and copper thickness; and conform to mounting and enclosure requirements (i.e. to connect power cords, connect to separate products, or provide secure attachment where disconnect due to motion or vibration are concerns). Although it can be quite advantageous for signal quality to place PCB connectors on or near the edge of the board, this can present issues for manufacturing. The greatest issue is how to best depanelize your boards during PCB assembly.
There are two primary methods of depanelization used today: scoring and routing. Scoring (sometimes called V-scoring) is the least expensive but less flexible method wherein a V-shaped groove is cut using a circular saw between adjacent boards. This method is difficult to implement when connectors are very near, on, or overhanging from the board edge. Routing, which may use perforations or solid tabs, allows for edge connectors but generates more waste material and is more expensive. Your contract manufacturer (CM) has to design a panelization scheme to facilitate the manufacture of your boards. This design must comply with the CM’s equipment and therefore may not be optimized for your connector requirements or even cost minimization. If your board shape is flexible, you can use it to optimize panelization and reduce costs. If not, you can lower the possibility of additional turnaround time for a redesign and eliminate unnecessary additional costs by following the guidelines below.
Panelization Design Guidelines for Common Connectors
▮ Place components with large connection areas away from the board edge.
Solder joints may crack or disconnect if placed too close to the V-groove line.
▮ Place connectors away from the board edge.
If this is possible, you may reap lower costs by being able to use V-scoring only.
▮ Use low profile connectors.
To use V-scoring, connectors with greater height must be placed further away from the board edge.
▮ Place all edge or overhanging connectors on one side of the board.
Do so may minimize the amount of tab scoring required and reduce material waste and manufacturing costs.
▮ For V-scoring, use jump scoring.
When using V-grooves, panels have a tendency to sag during wave soldering. Jump scoring, which is the addition of extended edges at the leading and trailing ends of a PCB array, can prevent this issue.
▮ For perforative tab scoring, use an adequate number of tabs.
3-hole tabs should be placed 1.5 in apart and 5-hole tabs should be placed 2-3 in apart.
▮ Make sure tabs that separate on a single break are collinear.
Otherwise, some tabs may not have clean breaks and could place enough stress on PCB layers to pull away lamination.
Following these panelization design guidelines should allow you to use any of the common PCB connectors without experiencing any manufacturing issues. As always, you should consult with your CM to ensure your design decisions can be implemented.
|Tempo‘s Custom PCB Manufacturing Service
At Tempo Automation, we employ board panelization so that your design intent and our capabilities are synchronized to optimize depanelization.
To help you get started on the best path, we furnish information for your DFM and enable you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on common PCB connectors or how to best design your panels for them, contact us.