UK SME: Die Devices – supplying bare die to the world

All of its products have one thing in common: they are 100% tested bare die, sold in small and medium quantities.

“We specialise in supplying die,” company owner and sales director Ben White told Electronics Weekly. “We are a niche supplier to aerospace, defence, medical and industrial customers.”

The company has eight employees and two identities: called Die Devices when it is distributing the die of other companies, and Silicon Supplies when it is a fabless chip company making its own die – more of this later.

Silicon Supplies PGA309

It traces its heritage back to the 1980s when White’s father Graham founded die supplier Mintech Semiconductors – a company which was eventually sold and gradually morphed away from its roots, according to Ben White.

In 2011, Graham White founded the present company, with Ben joining in 2017 and taking over when his father retired.

In the 80s, according to Ben White, bare die were mainly sold to make hybrid circuits, predominantly for military customers. Now there are a number markets that need bare die, including oil and gas, industrial, space and medical devices. Drivers include the need for operation at high temperature, exposure to corrosive environments or radiation or the need for miniaturisation.

Improvements in semiconductor manufacture have changed the game for bare die suppliers, according to White.

“In the 1970s and 80s, when device yield was not so great, everything was 100% tested on wafer,” he said. “Now process yields are so high that companies rarely 100% probe wafers. They just dice them them untested, package the lot, test, and throw away those packages that fail. At most, they sample probe before they package.”

As a consequence, selling bare die or even untested wafers has become an inconvenience to most chip makers because their production flows don’t even have a step at which wafers could be removed. Only for a few specific products, phones for example, are bare die shipped in large quantities.

“Bare die is a market that the mainstream manufactures don’t want to be in because it is very difficult for them,” said White. “We act as interposers between the chip maker and the customer.”

Part of Die Devices’ USP is knowing which chip company products can be supported and which can’t.

“We supply a selective range of die from branded manufacturers: Texas Instruments, On Semiconductor and ADI, for example,” said White.

TI AM26LV31E from Die Devices

As die are largely untested at wafer level, Die Devices has to start there, adding on the whole back-end chain to the manufacturers output.

At its Norwich HQ, it has three wafer probers – two six inch and one eight inch. “We don’t often see 12 inch wafers as that product mix leans toward higher volume digital,” he said. “If we do, we quarter them.”

To support its high-mix low-volume portfolio, the company uses a combination of automated and semi-automated die handling equipment. combining this with visual inspection, dicing and additional qualification via small batch assembly for further environmental testing.

“We do all the back-end to get die into the form that the customer can handle,” said White. Our typical flow has “even more processes than the normal wafer fab back-end”.

There are only a few things that cannot be handled in-house: “We outsource some lab work – for example scanning electron microscopy and destructive physical analysis,” he said.

It is not always possible to get devices in die or wafer form. “Even we cannot get some wafers, and we can get more than most,” said White. And this is where Silicon Supplies steps in.

The semiconductor devices designed by Silicon Supplies tend to split into two camps: trailing edge or leading edge.

At the trailing edge, solving obsolescence is the main driver.

Commercially, as semiconductor makers consolidate, the focus on die versions of a product reduces. Often a die previously available is obsoleted via corporate decision making, or the MOQ or cost to acquire it in die form becomes prohibitive.

As with packaged parts, when a die is no longer available, it leaves behind a set of customers with a very specific need – made worse with bare die because these don’t usually have the common footprint that a JEDEC package has.

Silicon Supplies designs replacements for obsolete die

“We are not usually talking high-end – these are not rocket science parts – but there is usually something unique and quirky about them,” said White.

The 74C906 is an example: a CMOS 4000 series derived hex open-drain buffer that can handle 15V. “It is not a complicated part, said White, “but people need it for 15V.”

Another is the LM3046 npn transistor array. “The very tight matching offered in VHF range is desirable and very niche,” said White. When the market heard it was available again, analogue synthesiser fans wanted it. “We even had to have some packaged into plastic.”

The company also produces a range of standard products intended as alternatives when an existing die supply becomes problematic.

Despite being made in the billions as a packaged part the 1N4148 does not have the same support in die form, so Silicon Supplies makes its own: “Data sheeted and stocked,” said White, “100% wafer probed 1N4148 die.” This last part is an example of devices that have become standard products for the company. Its list of standard products grows via its on-request commissions.

At the leading edge, the company recently made a miniature Schottky diode with a 210 x 210μm footprint for a medical eye implant.

Other modern parts are equivalents for devices not available in bare die from the first choice manufacturer.

This could be for technical reasons. For example, some die are now electrically trimmed into specification within the package, rendering them non-functional outside the package. “Manufacturers are not going to give away their electrical trim IP, so our solution is to implement the same function without trim – although you might get a different sized die,” said White, adding that the industry trends towards wire-bond-free package assembly also limits the viability of modern devices in the die form.

Most custom products developed are for sensing and power management: dc-dc converters, amplification and signal conditioning, and discrete diodes and transistors.

Another example, this time a mixture of old and new, is the company’s SiS4080A (left): a 1MHz silicon-on-insulator full-bridge motor driver standard part designed and made by the company as a more rugged direct replacement for industry standard HIP4080-type driver with improved switching capability.

It there anything the company can’t tackle?

It is not a question of not being able to do it, White replied. It is a question of expense and matching the project budget with available solutions. At the trailing edge to create an old DSP from scratch, for example, would cost so much that the customer is far better off to re-design the end-product instead.

Something similar is true for the bare die that Die Devices handles: “We don’t do a lot of high pin-count work. It is difficult to get equivalent test coverage – a typical high pin count for us is 60 I/Os,” said White. “We could theoretically probe test a high I/O FPGA or CPU, but the NRE would be huge.”

An on-going conversation with the engineering community is important, according to White. “We really exist to try to help people in this unusual world. We educate engineers who want to design with die and help them make their circuit viable from a die perspective,” he said. “Engineers can register and use our engineering portal – it is a safe place to get advice and check out part availability.”

For example, a designer needing to miniaturise something might have a particular part in mind, not realising that so few types of bare die are available.

“It’s best if we catch them early, before they have spent too much time and money. We will show them which parts can be supported, based on the functions they need,” said White. “What we suggest might often not be as perfect as the part they originally wanted, but it will be better suited in terms of availability for prototyping and do the job. Then we will try to supply them product through prototypes and into production.”

How does White sum up his companies? “Product enablers and educators in an often misunderstood but important niche market sector. Die-level applications drive innovation, so it’s vital that we empower this format.”