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Are you using the right SD card?

Originally designed to replace CDs and DVDs to distribute audio, SD and microSD cards are now commonly used in cameras, mobile phones and tablets. SD and microSD cards continue to be the removable storage device of choice, given their small size and capacity to retain huge amounts of data. However, with so many options on the market, how do you differentiate between them all and select the right card for your application? Most will be driven by price and capacity, but what about performance and quality? Should that be the driving factor when choosing SD and microSD cards? It really depends on what you want to use it for...

Industrial v Consumer cards

On the surface they look the same; identical mechanical design, same capacity and size. However, there are significant differences between industrial and consumer grade SD cards and flash devices in general. It is important to consider the impacts these differences have on reliability, endurance, compliance and total cost of ownership before selecting a device that is fit for your application.

It’s what’s inside that counts

Even when an SD card is opened (left) to reveal its inner workings, it will look fundamentally the same whether it's a consumer or an industrial card. However, some manufacturers, such as ATP, offer SiP (System in Packaging) which completely encapsulates all contacts and components.

Both cards will have a NAND Flash chip (the large block) and both will have a controller (the small block). The NAND Flash is where everything is stored; data files, presentations, music, pictures and so on. The controller is the brains of the device  – it's the part that communicates with the host device and manages the flash file system directory. The controller is also responsible for wear levelling, error correction and garbage collection so is vital in making the cards work. Industrial grade cards can typically operate in temperatures of between -40°C to 85°C, which is also known as wide temperature. Consumer cards typically can operate between -25°C to 85°C. So for applications that need to run in harsh environments for long periods of time industrial grade makes perfect sense.

Seek expert advice

There are so many card manufacturers that understanding which is right for your application can seem daunting. The technical team at Simms International can help by understanding your requirements, i.e. what the card is being used for, what data you are writing or perhaps it may be performance issues and the cards keep failing or data is being lost. We are often contacted by companies that have purchased consumer cards online, as the price is driving their choice and not the performance requirement.

Our experience has taught us that, if you understand the limitations of each technology and know the demands that are placed on the card (specific to the application they are paired with), you can avoid costly failures and save on engineering resource.

With different types of NAND Flash, it is important that you chose the right one for your application. The table below gives a brief outline of the characteristics of the different types of NAND Flash found in SD and microSD cards.

  SLC MLC TLC
Reliability highest medium lowest
Speed highest medium lowest
Warranty 5 years 2 years 2 years
Price highest medium lowest

 

SLC or Single Level Cell is the highest grade of NAND Flash currently available and is used for industrial. By industrial we mean; aerospace, defence, transportation, energy, telecoms, infotainment, medical marine, offshore, manufacturing type applications. SLC is highly reliable but expensive. SLC typically comes with a five-year warranty. SLC products are typically bespoke manufactured.

MLC or Multi-Level Cell is one of the most common grades of NAND Flash. This is also used in industrial applications and is cheaper than SLC. However, there is a trade-off between speed, reliability and durability. MLC is suitable for products that may need a change of storage every 18-24 months and are not heavily used. MLC can operate at wide temperatures and can be customised if industrial grade.

TLC or Triple Level Cell is a version of MLC, is used for the consumer market and is the lowest grade of NAND flash. The endurance and cost are low and it should not be used in any applications running operating systems or storing critical data. TLC is commonly found on the high street and online is widely available and cheap to manufacture.

Bridging the gap

Some companies have produced a type of NAND which bridges the gap between SLC and MLC. Performance is generally better than MLC but not as good as SLC. Manufacturer ATP, which uses aMLC, is a good example. The key differentiator with aMLC is the programme erase cycles (PE), i.e. the number of PE cycles is a number that a given device can sustain until problems occur. Each cycle causes a small amount of physical damage to the card which will accumulate over time until eventual failure. PE cycles for MLC range from 2-10K, aMLC 20k and SLC 60-100K, depending on the manufacturer.

Customisation

One of the underlying differences between industrial and consumer products is that industrial grade product is highly customisable. Vendors use advanced technology and algorithms to manipulate the NAND Flash. Examples include wear levelling, which moves write cycles around the chip so that cells wear evenly; on-device duplication, which reduces the volumes of data written and so lowers wear; redundancy, which reserves a portion of the device’s capacity to replace cells as they fail; and write optimisation, which stores data writes so they can be made in large chunks to reduce the number of write operations. Also, the controller used in industrial applications is far more effective than consumer grade. Companies such as Phison, Toshiba SMI and Hyperstone specialise in SD card controller technology.

Capacity

Industrial grade cards are generally not high capacity. There is still a requirement for 128MB cards with the highest topping out at 128GB in MLC. As SLC is more expensive cards tend to stop at 32GB. Given SLC performance characteristics this capacity for most applications would be more than enough (remember the 60-100K programme erase cycles). Consumer cards using MLC and TLC, on the other hand, are readily available in 256GB, 512GB and soon enough 1TB capacities. 

Features Industrial Grade Consumer Grade  
Operating Temperature -40°C to 85°C -20°C to 85°C Industrial grade has a superior operating temperature.
NAND Flash SLC / MLC TLC SLC is the highest grade, TLC the lowest. MLC sits in between.
Health monitoring Yes No Real-time monitoring that detects health status and provides product life expectancy.
IOPS Low High Performance measurement used to characterise storage (the higher the number the better).
Power protection Yes No Data will be kept secure in a sudden loss of power.
System in Package Yes No Protective covering leaving no components exposed to water, dust and humidity.
ESD resistant Yes No Electro Static Discharge resistant.
Advanced Wear levelling Yes No An algorithm that evens the erase count to prolong product life expectancy.
Autofresh Yes No Reduces the risk of data loss.
Dynamic Data refresh Yes No Checks for errors, removes the bad data and prevents data corruption, extends the lifetime.
Price High Low Only the highest grade components are used in industrial cards.
Controlled BOM Yes No The build of materials can be controlled over the lifetime of a project to avoid incompatibility issues.
Product registration Yes No Unique part code for your product to ensure supply consistency.
Lead times* 10-12 days 1-2 days Industrial is bespoke manufactured to the end users requirements and may need customisation.

 

*with the current NAND Flash shortages lead times may be longer. Watch Simms' short NAND Flash update video here.

Established in 1990, Simms International plc is a leading, specialist distributor of world-class memory and storage products to the UK industrial, corporate and consumer markets. The company offers a broad portfolio ranging from the latest technology to legacy products, providing NAND flash solutions and DRAM module technology designed for applications that demand the highest levels of reliability and endurance.

Comments

0 Votes
Simms International plc

December 8, 2017 13:18

@Dave66. Good question! Generally speaking, suppliers usually position their products based on specification rather than BOM. Also, it is difficult to compare various products based on NAND type alone as other components also influence the endurance and reliability of the storage device.
For that reason one would normally not find BOM or NAND information on the card and in some cases not even in the product specification. Worst case a customer may buy the same product over a period of time and get different NAND types while product name and spec do not change thus affecting the performance of the card.
What we do at Simms is to have discussions with the customer about the most suitable NAND flash for the application, what it is being used for, how long the data needs to retained, speeds etc. A controlled BOM can then be set in place to ensure the right/chosen NAND is being used for the lifetime of the project.

0 Votes
Dave66

December 5, 2017 08:53

Why is it that you never see "SLC, MLC or TLC" on the card itself.
How can you tell what you are buying ?
Dave

0 Votes
Simms International plc

December 2, 2017 13:32

@EdwardK, thanks for taking the time to read and comment on our article, you certainly know your SD cards! You make some really good points in your comments. We put together this article as we are seeing more and more companies embracing SD card technology but getting it wrong, with cards failing regularly, so our feature is to highlight the basic differences. We can get really technical at Simms (We are not just another disti – we know our tech). The points you raise are certainly very valid but when you dig deeper, there are some real technical issues that need to be taken into account. Take IOPS for example, you’re right they are high but one must take into account the performance difference depending on how the product is configured and optimised, which why IOPs vary greatly from one manufacturer to another.

With power loss protection, the protection mechanism and design usually differ from each other as there is no ‘standard design and validation for power loss protection’, so it’s down to the manufacturers own IP to design protection mechanism, which are then validated using test systems using different test scripts, pass/fail criteria etc.

ESD and wear levelling are common features in SD cards and not a major differentiator but nonetheless may be of interest to someone looking at NAND solutions for their system.
SIP and COB is an interesting one. All uSD cards and most SD cards are SIP designs but there are actually very few brands that actually manufacture them themselves – its exclusive to a few selected players. The majority of brands actually rely on turnkey solutions designed and built by 3rd party who have SIP manufacturing capability.

As for locked BOM (which we never say as it can’t be 100% guaranteed by the manufacturer) a controlled BOM however is more realistic. A multiple BOM qualification makes perfect sense to give you the safeguard for your application. We only partner with industrial manufacturers that offer a controlled BOM.

0 Votes
EdwardK

November 22, 2017 14:08

From a procurement perspective depending on application, host, customer usage profile our engineers can select NAND devices in the SLC, pSLC, MLC, TLC and even downgrade NAND. IOPS for cards these days is quite high with the more advanced controllers for all sorts of NAND. Hardware Power protection all serious brands have this feature i.e. Swissbit, SMART modular and Innodisk can withstand at least 30K+ and up for power cycling that we have tested them to extremes, we found Samsung surprisingly could withstand 80K power cycling also in their enterprise SSD lines we could make 250K power cycle and then we just stopped testing. ESD resistant products even consumer products are ESD safe over 15KV, i dont see that as a special thing. All cards these days have advance wear leveling, refresh - dynamic refresh mechanisms build in, it actually depends how the firmware and controller is set. The typical controller manufacturers Phison, Samsung, SMI, Hyperstone and for SSD also Marvell. Why is SIP or COB so special? All Micro-SD(HC) cards are made with SIP. MicroSD/SD card manufacturers buy NAND in wafer form, so need to build SIP or COB cards. As far as locked BOM, we would recommend to qualify multiple brands and make sure to usage latest cards for CO(s)TS down. Avoid at all time to be pinned to one brand or model....