PCB Assembly

PCB Assembly Costs: Factors Influencing Pricing and Budgeting Tips

A fabricated PCB is the work halfway completed. After the PCB is fabricated the components need to be assembled on the PCB. Without placing components, a PCB cannot function. Assembly of the PCB is a full-fledged task in itself. While PCB assembly might seem very difficult, EDA and CAD tools along with modern techniques have made synchronization and assembly much easier.

What is PCB Assembly?

PCB assembly is the process of placing components on the fabricated PCB by mounting and soldering the components. The assembly of components on the PCB needs to be well-planned during the design of the board. There are 3 files that vendors generally ask for PCB assembly, which are:

  1. BOM – BOM or Bill of material is the list of components to be mounted on the PCB. Generally, a BOM contains the part number, list of designators assigned to the part number, description, quantity of each part, type of mounting required, and other voluntary data like cost, reference number, and turnkey services. BOMs are a vital part of the PCB assembly, even small mistakes in BOMs can cause blunders to the PCB. But nowadays manufacturers confirm the footprints and part numbers for new assemblies.
  2. Pick and Place File – Pick and Place files are lists of coordinates of each component to be mounted on the PCB.
  3. Gerber File – Gerber file is generally required for confirming data in BOM and Pick and Place files.

Two Types of Mounting in PCB Assembly

  1. Through Hole MountingThrough hole mounting is the placing of through-hole components on the PCB. This type of mounting requires manual or semi-automatic assembly. However modern techniques like wave soldering have made automatic through-hole mounting somewhat possible.
  2. Surface Mount TechnologySurface mount technology is a method in which the through-hole components are mounted directly onto the surface of a printed circuit board. Since SMD components are the most widely used type of components among the two types, hence SMT is more popular. SMT can be automated or manual but for smaller components automated assembly is preferred.

A PCB may have both SMD and Through-hole components, but it is important to note that through-hole components need to be manually placed and hence might not be a viable option for mass PCB assemblies. But PCB assemblies with majorly through-hole components (like high-power PCBs) can be automated when assembled in bulk.

soldering

Factors Affecting the PCB Assembly Cost

PCB assembly cost is influenced by various factors, these factors are majorly dependent on the components used, design considerations, and economic factors.

The Choice of the Components

The nature of the components heavily affects the PCB assembly cost. Some of the cost-affecting factors due to the choice of components are: –

  • Size of the components – The size of the components is very crucial for PCBA cost. Mounting smaller and more unconventional components is generally much more expensive than regular sizes. For example, 0201 resistors are generally much more difficult and require expertise than 0805 or 0603 resistors. Further unconventional packages with smaller sizes fetch more PCB assembly price.
  • SMT or through hole mounting – As discussed earlier, SMT is mostly automated and Through hole mounting is generally manual hence SMT is much cheaper and faster than through hole mounting.  However for bulk quantities even through hole mounting can be automated. The mix of both types of components on the same PCB can increase the price unevenly as both manual and automated labour is required on the PCB.
  • QFP and QFN components – MCUs and some special components like network ICs use QFP ( Quad Flat Package) and QFN ( Quad Flat no lead) packages, assembling these components is much more expensive than general components. Things get a bit tricky in VQFP (Very thin quad flat packages) where the pitch of the ICs is very thin and hence requires much more precise placement fetching more PCB assembly cost.

Designing Considerations

The Design considerations of the PCB also affect the PCBA cost. Some of the PCB assembly price factors affected by PCB design are: –

  • The number of components – More the components that need to be mounted, the higher will be the PCB assembly cost, as the more components require more labor, time, and raw material (like solder paste) to mount the components.
  • Larger board size – Larger boards generally are more expensive to assemble than smaller boards. However, this trend might not be applicable to many vendors.
  • The complexity of the design – Assembling a higher density of components is more expensive than normally spaced PCB due to the required expertise and the precision required to place high-density PCB. Higher-density PCBs also require smaller components which again increases the PCB assembly price.

Economic Factors

Economic factors are tricky to handle. Making the assembly per unit as cheap as possible requires tactics and experience. Some of the PCB assembly price affected by economic tactics are –

  • Lead Time – Urgency or less lead time fetches PCB assembly cost. More lead time results in less PCB assembly price. The lead time cost may rise exponentially if a bulk assembly is ordered for a lesser lead time. Hence lead time must be factored in very carefully. PCBs with more through-hole components might have a higher lead time for bulk assemblies.
  • Assembly Quantity – Assembly quantity matters a lot and is a substantial fraction of the PCB assembly cost. Higher assembly quantities for PCB or joining two or more orders enjoy the benefit of the economy of scale. The setup fee and engineering fee are distributed over more PCBs which also reduces the PCB assembly cost. The higher number also reduced the PCB assembly cost for logistics. Inversely, we can say that a small number ( say for prototypes) will cost more per unit.
  • Addition of services from the same vendor – Services like fabrication and conformal coating if ordered from the same vendor, are eligible for heavy discounts. Old and good relations with vendors can also levy a discount on the assembly.   
  • Applying for turnkey services – Turnkey services from vendors generally avail the discount for assembly. Many times turnkey components are cheaper than ordering them on your own. Turnkey services reduce hassle and may also reduce the overall PCB assembly cost.

PCBA

Budgeting Tips for PCB Assembly

  • Using bigger or more general-sized components is much cheaper to assemble than smaller and unconventional ICs. It is not recommended to use very small components unless truly required. Smaller components might ease the design but will certainly need more PCB assembly cost.
  • Try to use as few components as possible. Fewer components on the PCB will result in lower PCB assembly costs (the quantity of the component should not be reduced at the cost of Mechanical integrity or Electrical integrity).
  • Use SMD or Through Hole components wisely as putting them on the same board is expensive. Using just SMD components not only reduces the PCB assembly price but also lead time as SMD components assembly is fully automated. However, if through-hole components are irreplaceable then try to use as few through-hole components as possible.
  • If the requirements allow, try to space components well. Densely placed components are expensive to assemble. A good practice is to predefine space constraints before designing PCBs. Many vendors have different thresholds of spacing distance between components, hence it is recommended to confirm with the vendor before applying constraints to avoid unnecessary PCB assembly cost.
  • Stretching lead time can help reduce the PCB assembly cost. If the requirement of the assembled board is not urgent, choosing a higher lead time for assembly would be a much wiser choice. For large quantities lower lead time costs are disproportionately high and many a time bulk quantities might not have even an option for urgent lead time.
  • Ordering fabrication and assembly from the same vendors costs much less than ordering them from separate vendors. Ordering fabrication and assembly in the same order can fetch a discount on the PCB assembly cost. Ordering from the same vendors also reduces the logistics cost which would have been incurred by different vendors.
  • Having more PCBs assembled in the same order reduces the price by the economy of scale. SMT assembly enjoys the potential of mass production. Economy of scale is a very powerful tool to reduce the PCB assembly price . For many vendors clubbing the bulk orders may also levy discounts.
  • Using services like turnkey from the same vendors can reduce the PCB assembly cost along with the components to be placed which reduces the overall PCB assembly price.

 

In a nutshell, it would be fair to say that the lowest PCB assembly cost would be incurred by a mass-produced PCB with only SMD components with optimal component spacing of at least 10 mils. However, quality must not be overlooked for a reduced PCB assembly cost.

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