Technology keeps getting smaller, and there is no reason for us to assume that trend will not continue into the foreseeable future. Designers and layout engineers are constantly under pressure to reduce board size, so we are sharing five common methods you can use to shrink your PCBs.
#1: Remove Testing Tools
Early drafts of a board often (and for good reason) include extraneous pads, headers, and even components to make debugging and testing easier. Once you are ready to scale the board down as much as possible for production, these should be the first to go. You no longer need an entire header for an off-board debugger or large pads on your microprocessor’s data pins to check with your oscilloscope, though you may still require some exposed pads if your product is going to be subjected to bed-of-nails type verification.
#2: Using Multi-Layer Circuit Boards
Most prototypes are done as two or even one layer boards. This gives you surface access to all components and traces to enable repairs, rework, and testing of a circuit. Once you are happy with the design and ready to shrink the board, moving components together can only do so much because you still need room to route. Moving to a four layer board is less difficult than you may think, and gives you much more room to run traces without taking up space on the outer layers. Even if you just use the internal layers for power rail pours, this can dramatically reduce the overall size of your board.
#3: Wi-Fi Bluetooth Combo Module
There are many pros and cons to using modules vs. discrete solutions for an aspect of your board, be it power conversion or wireless connectivity. This decision usually comes fairly early in the design process, but sometimes you will find the supposedly cost effective discrete solution costs too much in board real estate and want to make the switch. This could mean combining Wi-Fi and Bluetooth into a single module with an integrated antenna or switching to a switching regulator with an internal rather than external MOSFET.
#4: Circuit Boards with Heavy Copper
If you are allocating a significant amount of PCB area to thermal management or high current traces, you can shrink your board by using heavier copper. We tend to talk about minimum trace widths, but the true consideration is total trace area. The copper layer of a PCB is typically 1oz, so doubling that thickness to 2oz lets you run a trace half as wide with the same current capacity. 2oz is a common upgrade that can be handled by most board houses, but thicker copper is available. The industry considers heavy copper anything between about 4oz and 10oz, but boards can actually be made with copper up to 200oz. The situations in which such extreme weight is appropriate are highly specific, so you probably would have already been aware if you needed to go here, but taking a board from 1oz to 2oz is a very realistic solution to power issues on a shrinking board.
#5: Customize Circuit Board Size: Width & Length
Sometimes, the height of a board is a tighter restriction than the width or length. If your design uses tall components like electrolytic capacitors or headers, this can be an issue. When there is limited headroom, headers that accept wires at a right angle can be a good solution.
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If a large capacitor is cramping your style, you may be able to split that capacitance up across smaller components placed very close together. This tactic is typically not going to reduce cost, but it can give you the clearance needed in a tight space. For example, if you are using a 100uF leaded capacitor that has a footprint of 10mm x 10mm, you are using a total of 200mm2 because that area is required on both sides of that board. The capacitor is 25mm tall, which is too tall for your design. You could use 10 10uF capacitors in parallel, distributed across the top and bottom of the PCB, to reduce the total height to under 7mm, including the height of the board itself. Using several smaller capacitors is going to cost more than using one large capacitor, but it can be a useful tradeoff when space is truly the primary concern.
#6: Using Smaller Resistor & Capacitor Sizes
Since we typically populate the first version of a circuit by hand, we often use 0805 resistors and capacitors with plenty of clearance because they are easier to handle and allow more space to mark their reference designator on the silkscreen. Once the design is ready to be compressed, we can reduce the package size of those components. Although we have incredibly tiny components like Panasonic’s line of 01005 resistors and you can pull ridiculous stunts like placing resistors on their narrow side rather than flat on the board, it is rarely practical to go smaller than 0402.
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A standard pick and place machine will have a very high success rate with 0402 packages but may struggle with smaller components and decrease overall yield of your product. The power rating of components also tends to decrease with size, which may not be acceptable in your design. The aforementioned 01005 resistors are only rated to 1/32 of a watt, and 0201 1uF capacitors top out at about 10VDC.
#7: Shrinking Circuit Footprints
Once you’ve shrunk the components themselves as far as possible, you may be able to squeeze things a little tighter by changing your footprints. Tolerances are not as well defined in footprints as they are for mechanical drawings and tend to err on the side of generosity. The defaults for common footprints like 0805 need to cover as many variations as possible, so they may be larger than you actually need for your design. Check the datasheets of your specific components to see how much room you really should leave for each pad and modify your design accordingly.
You may be able to find extra mils in other common footprints, like your vias and annular rings for through-hole components. As long as you are aware of the precision specifications from your favorite board manufacturer, you can effectively determine how large those pads actually need to be – not just what is recommended by your CAD software. Do note that if you start modifying design rules, you will want to change those settings in your DFM checker to avoid getting hundreds of garbage errors that might distract you from an actual issue.
#8. Circuit Board Connectors
Connectors derail so many designs. They are unexpectedly expensive and large, and still tend to come into a design as an afterthought. Even the pads necessary to solder down a connecting wire seem disproportionately large compared to the pads for other components. While some connectors like USB or Telecom ports are not particularly negotiable, you can afford to be selective in your wire-to-board solutions. Header sockets are very common but do not provide much strain relief. Terminal blocks can give a great connection, but are pricier and quite later. Releasable right-angle connectors like the Lite-Trap family from Molex are used heavily in lighting for their low profile and ease of use, and are finding their way into more mainstream designs for the same reasons.
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Bonus: More Tricks to Reduce Circuit Size
Sometimes your constraints go beyond what can be accomplished with clever board design. The above tips should help you downsize a standard board that needs to shrink for cost reasons, but you may need to get creative for an extremely tight space or shape restriction. You may need to move to more board layers, use an exotic material like a flexible PCB substrate to fit along a curved surface, or even separate your design into multiple smaller boards that can be placed wherever they fit. If you feel you need a professional opinion, remember that our engineers are here to help.