There is an important but overlooked area of design that impacts costs for assembly and fabrication. Certain component packages can demand design practices that force higher fabrication costs, higher assembly costs, or both. These components tend to be in small packages, have high feature density, or both, even though the packaging they use is not unique.
If your goal is to design a product with minimized cost, then the component packages you use should be selected based on fabrication needs, inspection requirements, and expected yield. They also need to be selected for certain designs based on performance as certain products simply won’t be available in basic component packages. To keep costs in line and shave some costs off your assembly, consider whether you should omit these packages from your design.
Cost Reduction Adds Up at High Volume
When you scale production for a new product up to high volume, even the smallest cost reduction can add up to significant amounts of money. PCB fabrication costs tend to bottom out long before PCB assembly costs and component costs, so the typical instance where cost reductions can be seen is in these latter two areas. Cost reductions can be seen from simple component swaps before laying out the PCB, or by optimizing cost of a finished design just before production.
01005 and 0201 packages
While most assemblers have assembly capabilities to place and solder 01005 and 0201 SMD components, not all assemblers will charge the same per part for these placements. Depending on the assembler, smaller packages for SMD parts and equivalently-sized semiconductors might cost more per placement.
SMD component case sizes
Even if the per-placement cost is the same for these parts, the attrition requirements might be different. Some assemblers will require greater supply of these parts to account for attrition (losses) during assembly. Depending on volume and specific part type/number, you might see some cost reduction if you swap for larger case components, such as 0402 or larger.
The other factor surrounding case size relates to high-precision components. On some circuits, like ADC inputs, a design might contain 0.1% precision components, which are more expensive than standard precision. Some high-precision components may not be available in 01005 or 0201 packages as the part manufacturing tolerances are just too tight. If you can get away with 1% precision, you could swap for a larger or smaller case size and still see a cost reduction.
Another area where cost savings can be found is in array packages. Some components, like resistors or diodes, can come packaged in arrays, where multiple components or circuits are included in the same IC. These parts consolidate these parts into one placement, so they reduce the total part count for assembly.
This leadless package contains a diode array. It can cost more simply by being an integrated component, as well as due to its leadless package (see below).
In some cases, omitting an array package in favor of discretes gives you a better cost reduction than using the array package. The effect is mixed:
- Using the array generally allows for less space used on the PCB, and reducing the number of placements does reduce the per-board assembly price; however
- Discretes might cost less individually or at volume compared to the array component, so you might see lower component costs with little effect on total assembly costs.
The difference here depends on whether your fabricator is pricing based on SMD vs. standard IC packages, or whether all SMDs and standard IC placements are being priced the same per-part. Check both options and compare the cost difference if you’re looking for extra savings.
BGAs, QFNs, and QFPs
BGAs, QFNs, small leadless packages, and sometimes QFPs, are often called out on quote forms for assembly orders. For short runs, this may be a fixed cost, but above a certain threshold the cost will accrue per-placement. This is because BGAs and QFNs require X-ray inspection as part of quality control, and this adds to the total number of assembly and verification steps. QFPs might also add to cost, either per-placement or at a flat rate, due to the machine time accrued on higher-resolution optical inspection equipment.
The other factor relating to placement of fine-pitch BGAs is the fact that these boards will be more advanced and will use HDI buildup. Even if the placement and assembly costs are not higher, the per-board costs will almost certainly be higher due to the additional processing steps required to build these bare boards. Where possible, it is highly advantageous to select components that enable a conventional PCB build so that buildup layers are eliminated.
These aren’t the only areas where you can reduce costs. When you want to optimize your PCB design for lowest cost, including your board build and your BOM, make sure you use the complete set of CAD features in OrCAD from Cadence. Only Cadence offers a comprehensive set of circuit, IC, and PCB design tools for any application and any level of complexity.