Growing up, I always wanted to be bigger. Small guys like myself enviously referred to the larger guys as “the heavy cats.” I played football and spent a good deal of time in the weight room trying to qualify as a member of that unofficial fraternity. To augment my weight lifting, I also ate as much as I could, oblivious to the fact that there is a point where bigger is not better. As I’ve regrettably learned since then, there are many situations where a large size can be disadvantageous. For example, in electronics product development, the mantra is: the smaller the better.
As the demand for smaller and smaller electronic products continues to grow, surface mount device (SMD) package selection has become increasingly important in PCB design. As SMDs are typically available in several package types, you must consider not only size but also fan-out, via type, layer stackup, trace length, electrical characteristics and pad access or testability. Although these considerations should always be included as part of your design for assembly (DFA), there are options for SMD package selection that provide flexibility during prototyping and tips to help ensure the manufacturability of your final PCB design.
SMD Package Selection for Prototyping
In its simplest form, SMD package selection may be thought of as identifying a device that meets your functionality requirements while fitting within any space restrictions or limitations your design may have. However, you should also incorporate rules and guidelines for your board’s fabrication and PCB assembly; this is best done by including your contract manufacturer (CM) early in the design process. By collaborating with your CM before and during the prototyping process, you can utilize SMD package selection options that may reduce board turnaround time and cost.
One option that will simplify the board fabrication and PCB assembly of your design, while providing easier access for functional testing, is using larger component packages. In addition, you can also use a non-form factor or a larger board than required by the production design. Besides this relaxation of size restraint options, you may also want to use less-complex vias to the extent possible. This is not a recommendation to change the number of layers in the stackup, but instead to use pitch spacing that is easier to fabricate, for example from ball grid array (BGA) and chip scale packages (CSPs).
Another option that warrants consideration is whether to use a module-based design. This option will minimize the number of SMDs you need to select, reduce design revisions and lower the turnaround time and cost to verify your design. However, the time and cost trade-offs should be carefully weighed before opting for module-based prototyping.
PCB Design Tips for SMD Package Selection
The main objective of the prototyping stage of product development is to verify the functionality of your design. It is common to go through several cycles of design-manufacture-revision before the final design is settled upon and proven. The options discussed in the previous section are relevant for facilitating functional testing for preliminary designs. Once the design is proven, it will be necessary to create a final PCB design, including the actual SMD packages for the components that will be used.
This final PCB design for prototyping is actually the production design and the design objective for SMD package selection shifts to component optimization. Although SMD package selection objectives may differ, the DFA requirements for prototyping and production must always align with your CM’s equipment capabilities and processes. Below are a few tips that can be applied to help you take advantage of SMD package selection flexibility to improve your product development, whether you’re at the prototyping or production stage.
Tip #1: Choose the largest SMD package that meets your requirements.
Most SMDs are available in several package sizes. For example, an integrated circuit component may be available in quad flat no-lead package (QFN), BGA, CSP or other larger packages with fan-out, such as quad flat package (QFP). The larger components are easier to assemble as pitch spacing is greater and trace separation is wider. Larger components are also more accessible for testing.
Tip #2: Research SMD package selection availability.
It is important to ensure there are sufficient components available on the market to meet your prototyping and production needs. If in production, it may be a good idea to stockpile components to guard against future shortfalls that can significantly reduce or halt your product production and delivery.
Tip #3: Have a backup plan.
It is a good idea to have an alternative component with the same SMD package that can be easily substituted without major design revisions in the case of a component shortage.
Tip #4: Choose the best via option
From the PCB manufacturing perspective, the best SMD routing is the simplest to implement. Knowing your fan-out options and choosing the least complex via type that works with your design will save you time and cost during manufacturing.
Tip #5: Verify your CM can and will employ your via options.
All vias are not created equal, especially from your CM’s perspective. For example, some CMs might discourage you from using via-in-pads or refuse to guarantee boards if you insist on using them. Therefore, you need to work with your CM to confirm your design requirements are met and the associated via type(s) can be instituted.
As electronic product development leads to smaller and smaller devices, SMD package selection will continue to be a major consideration for your PCB design, prototyping and production. At Tempo Automation, our advanced software-driven PCB manufacturing operations are equipped to meet any SMD package selection you require to enhance your PCB design and development.
|Tempo‘s Custom PCB Manufacturing Service
And 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 SMD package selection or the PCB design options available for component selection during prototyping and production, contact us.