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How Small Is Too Small for Passives?

As manufacturers reduce the size of cell phones and other portable equipment, while cramming the devices with the latest features, passive component manufacturers are reaching physical limitations in shrinking package sizes for parts.

Technological breakthroughs in materials and manufacturability are likely needed to advance packaging shrinks, according to component makers.

"Sometimes a breakthrough on a raw material enables you to go to the next step," said David J. Valletta, executive vice president worldwide sales for Vishay Intertechnology in Malvern, Pa. "Passives is a materials business. Whenever there is an improvement in materials, it improves the component technology."

Component design factors also play a key role in shrinking package sizes. "The holy grail in passives has always been getting the same level of capability or more capability into a smaller package," noted Valletta. "When you try to do that, it involves design aspects. You have to look at the internal design, layers, electrodes, etc. It also could involve different raw materials and different formulations that give higher performance with less of it.”

Most suppliers agree. "Today's packaging technology, which could be true of any dielectric, is facing the obvious technical constraints of just following the same basic designs for smaller and smaller case sizes," said Fernando Spada, vice president, tantalum product marketing, Kemet Corp. in Greenville, S.C. "You can look at how each part is constructed today and how the anodes and cathodes are put together, and we're starting to face some physical limitations in terms of mechanical constraints," he added.

However, there are issues when moving to new materials and processes. Spada noted that if the materials solution is different than traditional processes, for example, capacitance embedded into the circuitry, then the questions become "what materials will be needed to meet this expectation, and how do we manufacture this at volume and cost effectively."

Kory Schroeder, director of marketing, at Stackpole Electronics in Raleigh, N.C., said there needs to be a technological leap in order to achieve smaller package sizes for resistors. "I don't know if we can go much smaller realistically at this point," he noted.

Schroeder believes the next step will be function integration, where the entire function of several resistors is placed in a single unit.

"The holy grail in passives has always been getting the same level of capability or more capability into a smaller package," said David J. Valletta, executive vice president worldwide sales, Vishay Intertechnology.
Currently, the most popular and cost-effective case size for many capacitor and resistor manufacturers is the 0402. "It's small but a proven package size,” said Valletta. Typically, this case size is used in handheld game systems, mobile phones, portable computers, disk drives and tablets. ”Anything that is small and needs more functionality in a smaller space," he added.

In general, the most popular package sizes for resistors and ceramic capacitors are the 0402, 0603, 0805 and 1206. Tantalum capacitors are designated as EIA standard case sizes (including A, B, C, D and E), but suppliers also offer lower profile versions, including S, T, U and V case sizes. The most popular thicknesses are the 1 and 1.2 mm, but no more than 1.9 mm, according to Spada.

Smaller is not always better

Buyers should be aware of several drawbacks associated with the smallest passive devices, including difficulty in placing the components on the board, which adds cost, and higher tags.

Currently, the smallest chip package size available for passive components is the 01005, but only the most space-constrained products have opted to use it because it is difficult to handle. It also comes with a price premium, and not all suppliers offer the size.

Even the 0201 package size, which has been available for several years, has not really taken off. Most suppliers say the 0201 also comes with a price premium, and like any other component, prices will not fall until there is high-volume demand.

Not all OEMs need an ultra-tiny package size. It depends on their board real-estate constraints. In some instances, height may be the real concern, but in other cases, the x/y area is smaller so the available real estate to place components on the board is shrinking.

Additionally, there are a lot of challenges when it comes to the 01005, ranging from handling difficulties and manufacturing issues to higher price tags and lack of demand, said suppliers.

"Everybody assumes as you go smaller, you use less material and the pricing will get better just like the 1206, 0805 and 0603. With the 0201 it stopped," said Schroeder.

The 0201 has a significant price premium because it is difficult to manufacture, according to Schroeder. "It will be more so with the 01005 because there are tons of questions as to how you get that resistor to customers in a manner that they can handle it, place it on the board, solder it and test it."

"For some devices like thin-film resistors, it doesn't make much sense to offer a 01005 package size; the maximum ohmic value would be a few kiliohms,” said Jerry Seams, global applications engineering director, TT electronics, Fixed Resistors.
Product development teams, including buyers and designers, also need to keep in mind that smaller components cannot handle as high a rating as larger devices, and for some devices it simply does not make sense to offer them in a 01005 package. The smaller the resistor, the less current it can handle and for capacitors, it cannot handle as high a capacitance/voltage (C/V) value.

This is particularly notable in thin-film devices. "Because there is less real estate, it limits the maximum ohmic value range of the resistor in a thin-film device. That's because thin-film technology has a more limited sheet resistance range available to it than thickfilm," said Jerry Seams, global applications engineering director, TT electronics, Fixed Resistors, based in Corpus Christi, Texas.

As an example, TT's PCF precision chip resistor offers a maximum ohmic value of 22 kiliohms for the 0201, but it can go to megaohms on the larger sizes.

"At least for thin-film precision resistors, you've reached a point of diminishing returns," Seams noted.

Equipment is another big issue. "All of a sudden, the equipment you use to handle a slightly larger or thicker part number has to be physically configured to handle something smaller," said Valletta. “If you have a machine setup to handle 0805 packages, it has to be configured or at least capable of handling 0201, but it also has to be modified to be gentler."

Schroeder added it also requires the device to be placed much more precisely, which increases manufacturing cost and time to market.

Historically, the passive component industry has continued to shrink package sizes, and there is no reason to think that it will not continue. Suppliers believe that the capability to develop smaller packages is there but the need is going to be dictated by market demand and the capabilities of customers.