What to consider when sourcing smaller crystals

Understanding the constraints of miniature quartz crystal components can help purchasers to balance price and specification needs, says Golledge.

Increasingly, product designs call for smaller and smaller quartz crystals. Since the early 1980s quartz crystals have reduced in package volume by an astonishing 99.5 per cent and today, for the most miniature designs, a crystal package of just 0.46mm³ is possible. There are multiple challenges posed by this reduction in size and it can be helpful to be aware of the engineering constraints when sourcing smaller quartz crystals.

The engineer’s perspective
Designing in a cutting-edge ultra-miniature crystal is no small task. Reducing the size of a quartz crystal can cause a host of unwanted effects such as reduced motional capacitance and trim sensitivity due to reduced electrode size, higher motional resistance due to a reduced active area of the crystal, drive level dependency of the resonant frequency, and increased minimum frequency. Combatting many of these effects requires careful circuit design and depends on strict crystal product specifications.

The purchaser’s challenge
Ultimately, the purchaser’s challenge is very different to that of the engineer when sourcing tiny crystals. Purchasers must balance three core, oftentimes competing, aspects. These include the need to meet strict product specifications and ensure supplier quality whilst achieving the lowest price possible.

In addition to inflexible product specification demands, there can often be price implications of specifying the latest generation of quartz crystals. Due to the cutting-edge nature of some ultra-miniature frequency components a purchaser will also want to be assured of their supplier’s quality credentials.

So, what can a purchaser do to meet the challenge presented by sourcing ultra-miniature quartz crystals?

Specification versus costs
Pricing structures within the quartz crystal market tend to depend on how well developed a product package is, with three loose categories: newly-developed products, well-established products around five to 15 year old, and those products over 15 years old that are no longer recommended for new designs. Whilst it is easy to assume that newly developed products will be the most expensive, there can also be cost impacts when purchasing products which are no longer recommended for new designs.

Well-established lines with few custom specifications tend to be the most cost-effective, however, thanks to advances in manufacturing technology, some newly developed products can beat price structures of well-established products. It is always worth asking suppliers for alternative lower-cost crystals that are close to the required specifications in case your designers can work with these.

Finally, knowing the largest purchase quantity available will help to stave off some of the price risk when sourcing ultra-miniature quartz crystals. Where possible always let your supplier know your usage forecasts.