The younger version of me always had a passion for staying in shape. Hours of tennis and basketball and miles of running did the trick. At 6’1”, 175 pounds, that version of me could eat entire pizzas without gaining an ounce and could jump over tall buildings.
Ah... the glory of having that shape.
Switch to the current version of me. The hours of tennis and basketball have diminished. Miles of running still happen but instead of the jackrabbit I once was, I’m more the tortoise. No more eating entire pizzas. Instead, it’s fruit and veggies and Greek yogurt. But, er, the current version of me has a new and different shape. I wonder if there’s a “dad-bod” of PCB shapes, too?
A Standard Approach to PCB Shapes Wins Friends
Standard rectangular and square board shapes rule the magnificent world of PCB design. As irregular shaped PCBs have become more common, though, the grand order of rectangular PCBs has become slightly diminished. Many times, unconventional PCB shapes occur because of the need to fit into oddly shaped enclosures.
Standardized PCB shapes yield benefits. You can gain surface area with the same overall dimensions. Since assembly houses measure at the widest and longest points of the PCB, rectangular shaped PCBs provide an effective solution by maximizing the available area. As a result, using a standard rectangular or square shape keeps manufacturing costs from increasing. Standard PCB shapes also provide the space needed to route traces and to place components.
Take the Plunge into Different Shapes
Matching the form factor of a new product enclosure often requires an innovative approach to PCB shapes. Within the innovation, matching the form factor also relies on transparent communication between ECAD and MCAD software. A product design may require the use of a round, triangular, oval or other shape PCB to achieve the aesthetic or ergonomic appeal of the product or a smaller, denser board that solves profile issues.
Ensuring the board works is priority number one, after that meet the requirements the shape calls for.
As you design for manufacturability, your software should support the integration between ECAD (Electronic CAD) and MCAD (Mechanical CAD) tools. Using integrated ECAD and MCAD tools helps speed up the design time by allowing you and your team to make changes on-the-fly. This integration of ECAD & MCAD tools allows you to define board shape, establish board dimensions and import component models.
Your design software should allow you and your design team to manage your board shape through version controls and collaborative tools. Computer-aided design (CAD) and 3D design tools ease the process of moving from the schematic and product design to the prototype stages. Those tools provide the visualization that you need to verify clearance requirements for the PCB, components, and the proposed enclosure.
Proper Trace Widths Ahead
Follow common design rules for PCB traces used on both standard and non-standard board shapes. Your trace lengths should remain as short as possible to prevent parasitic effects and impedance mismatches. To avoid interference with high speed signals, the traces should bend at 45º angles. 45° angle also shortens the electrical path between components and is useful for acid traps, reflections at corners, and overetching.
The width of your traces impacts the amount of current flow through the circuit. Although your PCB design software includes tools for determining the width of your traces and the distance between the traces, components, and adjacent traces, you should work within the manufacturer’s minimum specifications. Most fabricators accept 6 mil spacing and some may work with 3-4 mil spacing.
Crowding pads and traces onto a board pushes manufacturing costs higher because of the precision equipment needed for manufacturing. Standard rectangular and square boards allow you to maintain the minimum spacing requirements established by manufacturers. Because standard-shaped PCBs conserve board space, you can also control costs by using larger holes and annular rings.
I was on a Panel Once
You can replicate your PCB several times on a larger board through panelization. Fabricators use this method to control costs. Placing the maximum number of boards on the largest available panel size allows pick and place machines to place components on the PCBs within one setting. The use of standard rectangular and square boards offers the best opportunity for achieving good panelization. Consult with your fabricator about their preferred size of panel and then build your design rules.
However, panelization also works for irregular or complex shaped PCBs. Although the use of complex shapes complicates the panel layout, you can use the Breakaway-Tab Panelization Method to increase the board count on the panel and ease the process of depanelization by designing arrays with solid tabs between the boards. The 3- and 5-hole perforated tabs align with the routing space between the PCBs and prevent any leftover material from protruding past the PCB edge. Depaneling with the tab method occurs through the use of a depaneling router or a laser-cutter.
You can also use the V-groove Panelization Method if no components extend over the edge of the board. V-groove panelization requires cutting 1/3 of the board thickness from the top and another 1/3 from the bottom with a 30° to 40° circulating cutting blade. The method requires that 0.05 inch clearance exists between component and the center of the V-groove. In addition, larger-sized capacitors must mount no closer than 0.25 away from the score line.
Optimizing shapes for panel efficiency can drastically improve manufacturing yield
As with the Break-away Tab method, the use of V-grooves can weaken a PCB during wave soldering. The process of wave soldering results in surface tension that can pull pre-heated PCB material away from the groove.
Complex Shapes Require Care
Complex and irregular-shaped PCBs work. No large disadvantage exists when designing a circuit board that has a different geometric shape. You do need to, however, give additional attention to your traces, components, and the use of space on the board. A round PCB—for example—may have empty space because of the shape.
Using a different-shaped PCB requires consistent, precise communication with assembly houses. While some assembly houses charge additional fees for working with a complex or irregularly shaped PCB and increase the number of days for producing the board, others provide the work as part of a standard price package.
With Cadence’s active and ever-expanding roster of tool capacities for PCB design and analysis, you’ll be sure to create designs with whatever PCB shapes are necessary. OrCAD’s PCB Designer is assuredly going to allow you to layout and push a board to production with ease and maximum efficiency.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.
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