Electronic equipment cost is more than Bill of Materials cost

Hafeez Najumudeen & Gabriele Fulco
Product Marketing Manager & European Product Marketing Manager for Sensors
cost of assembly must be considered as well as cost of bill of materials
When considering the overall cost of manufacture, it is essential to look at more than just the Bill of Materials cost - assembly time is also a major element.

When calculating the total cost of the Bill of Materials, how many buyers consider the cost of assembling the components alongside buying them? For example if one connector is quicker to assemble to the board by 2s, over a run of 500,000 units that adds up to a time saving of nearly  278 hours or 35 working days. Similarly, a pre-wired component can be installed anywhere in a system without the need for a PCB – which can save considerably more than the small premium for the device itself.

FPC connectors

FPC connectors are a popular and space effective option for interconnecting PCBs and connecting boards to displays. Growth in wearable electronics is giving this technology a further boost. However, some FPC connector designs require fewer steps to assemble than others.

Many manufacturers supply their connectors with the latch in the closed position. This means that it has to be opened as a separate (normally manual) step before the FPC itself can be inserted. The reason is that most FPC connectors have the locking mechanism at the front of the connector, where the cable is inserted. Omron’s patented mechanism places the lock at the back of the connector. It's connectors can be shipped with the lock in the open position – eliminating a production step. The time saved is – just 2s per connector, but on a high volume production run this can add up to a lot of time (Table 1). This has the further benefit of reducing the risk of the cable movement lifting the locking mechanism in use.

Many FPC applications are made in huge volumes, and just reducing the assembly process by a single step can bring about major time savings.

 

Time saving

2s per connector

Batch size

500K

Total time saving

1 million seconds

= 16,667 minutes

= 278  hours

=  35 working days

Sensors

Similarly, components are sometimes located off the main PCB and will sometimes need a separate subsidiary PCB of their own. Sensors are often affected – for example the sensor that confirms the presence of a cup in a drinks vending machine will need to be located in the drinks dispensing area. The main PCB will almost certainly be located in the middle of the machine where it can be well protected.

Typically this application will require a photomicrosensor, a compact optical sensor that senses objects or object positions with an optical beam. The transmissive photomicrosensor and reflective photomicrosensor are typical photomicrosensors. The transmissive photomicrosensor devices (also known as slotted photomicrosensors or photo-interruptors) incorporates an emitter and a transmissive that face each other. When an object is located in the sensing position between the emitter and the detector, the object intercepts the optical beam of the emitter, thus reducing the amount of optical energy reaching the detector. The reflective photomicrosensor incorporates an emitter and a detector. When an object is located in the sensing area of the reflective photomicrosensor, the object reflects the optical beam of the emitter, thus changing the amount of optical energy reaching the detector.

Variants for detecting objects moving horizontally or vertically through the sensor are available, as well as extra-wide styles and dust-proof versions. All styles are available in Dark-On and Dark-Off formats. Dark-On photo micro sensors switch on when no object is present in the aperture, whilst Dark-Off devices are activated when object is present.

Photo-microsensors aimed at this kind of application in office equipment, home appliances, vending machines, arcade games and medical applications, are now offered pre-soldered to a connecting cable. They can be bolted onto the equipment housing in a suitable location and connected back to the PCB. This reduces cost by eliminating the need to create a specific separate PCB assembly for the sensor, and increases reliability.

Cost is king

Most buyers understand that the true cost of ownership starts rather than ends with the purchase of the device. When comparing two apparently identical proposals from alternative vendors, though, it is well worth a discussion with the production as well as the design department to see if there are differences in the assembled cost of the component.

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