Technical director at Anglia Components, David Pearson, explains why specifying smaller chip passives can eliminate future obsolescence worries, saving both time and money down the line.
It is an inescapable reality that the industrial distribution market for chip passives represents a very small proportion of global consumption. Most chip passives go into consumer electronic products that are manufactured in massive volumes. Consequently, it makes sense to specify the chip passive sizes that are most widely used—even if that means going for a smaller device than you would ideally like.
Identify the sweet spot
Globally, the largest percentage, by volume, of the chip passive market use 0201 size and below so it is no surprise that there is a long-term trend for manufacturers to discontinue, or make fewer batches of, the larger chip passives: 1206, 0805 and 0603. We are already witnessing managed obsolescence on some of these larger chip sizes.
The fact that the larger sizes consume more material and production capacity creates an active disincentive for manufacturers to produce them. For example, reducing the size from one platform to the next has historically more than doubled production yields for the equivalent amount of raw material. And although currently there isn’t a shortage, each time the supply chain tightens, we always see greater pressure on the larger sizes than the smaller.
Recently capacity availability has improved, however, manufacturers are still not recommending larger sizes for long term designs.
Look to downsize
Currently 0402 and 0201 are the sizes that Anglia recommends for new designs. Larger sizes are still available, but information from manufacturers is that they will become increasingly scarce longer term. You could be caught in an endless cycle of lengthening lead times, restricted capacity and rising prices. To avoid this, consider moving to smaller sizes for current and new designs if they are compatible with your voltage and value requirements. If you have a design that includes larger chip passives, which you intend to continue producing for some time, it is worth considering a redesign just to get rid of them. Redesigns are expensive, but line stops even more so and eventually you may simply be forced to redesign your board anyway.
Most sub-contractors can place 0201 and even 01005 devices, however, reworking boards with 0201 and 01005 chip passives can be challenging. It is therefore important to understand any potential yield issues due to scrappage before selecting which chip size to specify.
Investigate polymer alternatives
Not every voltage and every value is available in smaller chip sizes because of the physical constraints of the material. Anglia’s advice is to move to the smallest chip size available in the value and voltage required, however, on high cap MLCC values above 1µF, polymer capacitors may provide an alternative. Although they are larger and more expensive on a same value and voltage comparison, they do not suffer with the same DC bias characteristic that MLCC capacitors do, where capacitance decreases as voltage is applied. This means it is possible to use a lower capacitance polymer capacitor, thus giving an overall system cost saving. This is especially true where multiple MLCCs are being used to achieve a high capacitance value. However, polymer capacitors are polarised so they are not an option in circuits that may see a reverse bias or
in AC applications.
Don’t get caught out
In practice, the largest manufacturers follow the demand of their key customers in the consumer segment and this defines where they allocate capacity. Thus, if you include any device on your BoM that isn’t standard and widely available, you’re taking a risk. If there are alternatives that can be substituted with comparatively little pain, it is an unnecessary risk. As manufacturers discontinue or reduce production capacity on larger size chip passives, buyers need to look at their options to ensure they don’t get caught out with inventory shortages, price increases and unworkable lead times.