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Automated Reliability Prediction Procedure (ARPP) FAQs
BASIC LICENSING INFO
Is the Telcordia SR-332 methodology applicable to me?- SR-332 contains generic reliability predictions for all types of electronic devices (resistors, capacitors, connectors, ICs, etc.) and is used to predict the overall failure rate of electronic products or systems used in any industry (telecom, medical, military, etc.).
- The ARPP software tool automates the prediction calculation by allowing the generic failure rate for each device to be multiplied by stress parameters for temperature, electrical stress, device quality level, and environmental factor.
The ARPP is currently the only hardware prediction tool based on Issue 4 of SR-332, Reliability Prediction Procedure for Electronic Equipment. The ARPP is priced much less than a single copy of a larger reliability software package, and it can be used by any employee of the purchasing company. The ARPP takes advantage of common user familiarity with Excel® spreadsheet software; therefore, the ARPP does not have a steep learning curve in getting started with reliability prediction. How difficult is it to use the ARPP tool?
Because the ARPP is an Excel spreadsheet, it is much easier to use than the more complex reliability prediction software, which often requires extensive training. Using the instructions and examples provided, the user can be up and running ARPP reliability predictions within minutes. How do I know the results will be recognized by industry?
SR-332 has a long history of use within and outside the telecommunications industry. Issue 4 provides the most up-to-date and accurate estimates available on the market today. The document was developed with extensive industry input. How does the ARPP’s cost compare to other software reliability prediction tools?
The ARPP provides an alternative to the expensive software programs on the market. The ARPP provides a cost-effective solution for calculating reliability predictions for small- and medium-sized manufacturers of electronic boards and subassemblies. If I purchase the ARPP, do I need to also purchase SR-332?
The ARPP is only licensed as part of a package with SR-332. The ARPP cannot be purchased separately. Is the SR-332 document available for purchase without the ARPP?
Yes. SR-332 is available as an individual product. The ARPP is sold as an Enterprise License. What does that mean?
An Enterprise License is an agreement that allows your company to distribute the ARPP to all employees in your company. This means you don’t have to buy multiple single-licenses to provide the tool to different groups and/or business units within your organization. This saves you money. If I request a license fee quote, do I have to buy the ARPP?
Requesting a quote does not obligate you in any way. How long does it take to get a license fee quote?
A Customer Service Representative will contact you within two business days or less of your request. We will honor your quote for 30 days.
USING THE TOOL
When I open the ARPP Excel® tool, I see a message asking if I want to update links. I say "yes", but it comes back and says it cannot and asks if I want to continue. What should I do?The tool can be used with links to connect to a parts database that users have developed to simplify importing device information. (See the “Guidance” tab and “Initialization” heading for information on how to map a database to the tool.) Most users do not use this feature, so you can choose “continue” without updating the links at startup. The tool will function properly. What is necessary for the SR and tool to help me predict the reliability of my products?
The SR is the preferred method for predicting the reliability of electronic equipment, the software calculates the reliability based on the electronic components. All the customer needs is a Bill of Material (BOM) that contains the device part number, description, quantity, reference designator, device manufacturer and manufacturer’s part number. Actual reliability calculations, however, are not performed by Telcordia and can be performed by independent contractors. Does the ARPP provide a parts database?
Experience has shown that even the most expensive reliability prediction programs cannot maintain an accurate up-to-date parts database. As a result, the parts contained in such a database are typically old parts that do not reflect current technology. A better approach is to develop one’s own parts database that reflects the current parts used in one’s own manufacturing facility. The ARPP provides the capability to import a user’s own database of components with internal part numbers assigned to the various SR-332 component classifications. As first-time parts are used in the ARPP spreadsheet, these parts can than be added to the user’s database. What is meant by the statement, “A better approach is to develop one’s own parts database that reflects the current parts used in one’s own manufacturing facility.”?
The statement about “one’s own parts database” refers to the spreadsheet’s capability to process an association of internal parts numbers to generic RPP device category and subcategory. The user can specify an Excel file that lists the RPP category, subcategory, and complexity for each internal parts number. In this way, whenever an internal parts number is entered in the spreadsheet, the spreadsheet automatically fills in the appropriate generic failure rate without the user having to select a category, subcategory, and complexity. This is especially useful if the user will be entering bills of materials, which specify internal parts numbers. Does the database have a facility for using both internal part numbers and manufacturer part numbers, or do you have to use only one or the other for a given component?
The database must be constructed so that a given component uses either an internal part number or a manufacturer part number. However, it is OK to have some components use an internal part number and others use a manufacturer part number. Is there a device failure rate database included in the software?
No, but you can enter a part number, description, and quantity, then use the tool’s easy-to-use drop down menus to categorize the device by Category, Subcategory and Complexity. And since it's an Excel-based spreadsheet, it is much easier to use than other prediction tools and allows for rapid cut-and-paste of input data. Does SR-332 call for tests at the limits of a parameter that is specified in the data sheet for the part that is being tested?
- SR-332 does not specify the test conditions of any part to the device data sheet limits. Rather, SR-332 predicts the estimated failure rate for a system (or circuit pack) based on the sum of the failure rates of the individual devices in the system when operating under “normal” use conditions. SR-332 does provide temperature and electrical stress multiplier values to be applied to each device, but these stress parameters should be based on normal operating conditions and not maximum “worse-case” conditions.
- The goal of SR-332 is to estimate the average steady-state failure of a product in the field under typical field operating conditions.
Table 9-4 from SR-332 has a high-level description. More details on a quality assurance program for components, including qualification tests are found in GR-357, Generic Requirements for Assuring the Reliability of Components Used in Telecommunications Equipment. You would need to work with your components suppliers to see if they operate under a quality system that meets the described characteristics. Is it permissible to use drag-and-drop editing in the ARPP?
No. Drag-and-drop editing (moving cells in a worksheet) can alter formulas in the cells of the tool. It is highly recommended that users turn off the drag-and-drop editing option. To do this:
- On the Tools menu, click Options.
- On the Edit tab, clear the “Allow cell drag-and-drop” check box.
It is likely that drag-and-drop editing was used. Drag-and-drop editing (moving cells in a worksheet) can alter formulas in the cells of the tool, resulting in the disappearance of results. It is highly recommended that users turn off the drag-and-drop editing option. To do this:
- On the Tools menu, click Options
- On the Edit tab, clear the “Allow cell drag-and-drop” check box.
There are no output reporting capabilities aside from the capability to copy the worksheet contents as needed. The worksheet contents should be pasted using the paste values option to protect the Telcordia formulas. The user can then format the output as needed. (The paste formats option can be used to preserve the formats of the original file). I have Windows 2007 and cannot save my changes in the Excel Spreadsheet.
When using Windows 2007, open the ARPP and save as a Macro-enabled 2007 Excel file. The new extension should be .xlsm.
I recently installed Windows 2007 and am having a problem launching the tool.
In Windows 2007, a Security Warning message will appear at the top of the screen (below the tool bar). Click on the Options button and a dialog box will appear. Click the button “Enable this Content” and the tool then works and gives results for the device and total unit level. Please keep in mind that You must Enable Macros each time you open the ARPP. You must perform this step each time you open the ARPP to work on your worksheet. I have Excel 2008 and am having trouble enabling the macros.
Do not select “Enable any Links”.
In Excel 2008, select OPTIONS at the top of the tool, then select “Enable This Content”. Do not select “Enable This Content” in the Links section in the lower half; otherwise, it will look for the link. Does the SR-332 tool provide MTBF data for any specific supplier’s product?
SR-332 does not contain failure rate information on any given device manufacturer’s product. Rather, SR-332 provides “generic” failure rates for each category of devices. SR-332 is a tool to estimate the failure rate of a product based on generic component failure rates. Can I get MTBF from the Excel spreadsheet for a unit (e.g., an RF Amplifier with multiple PCB assemblies interconnected via cables and or pins)?
Yes, SR-332 and the associated Excel tool will fulfill these needs for MTBF results. The SR-332 document and ARPP tool specify device failure rates in FITs (failures per billion hours) since FIT rates of the individual devices can be added together to get the total FIT rate for each circuit board or complete assembly. The MTBF for each board or complete assembly is simply the inverse of failure rate in units of hours. The ARPP tool only shows MTTF results instead of MTBF because the tool does not know if these calculations are for a repairable system (MTBF) or non-repairable system (MTTF). For calculating board-level and complete assembly predictions where hardware redundancy does not apply, MTTF and MTBF are one in the same. Therefore, please use the MTTF results shown in the ARPP tool for your MTBF results (i.e., MTBF = MTTF). . Does the SR predict the failure rate for a printed circuit board (PCB)?
Yes, to a degree: it calculates the predicted failure rate of a unit or assembly by adding up the failure rate of the individual electronic components on the circuit board. It does not calculate a failure rate for the "bare" board itself (i.e., PCB without components). The bare PCB is a passive board, and the SR does not count solder connections, which are considered workmanship related and not reliability related, which has a time-to-failure distribution. How does device complexity apply when using the tool?
Device complexity applies to some devices in order to take the complexity of the device into account. The ARPP tool does not contain device manufacturer data. The complexity of the device must be obtained from the manufacturer's data sheet. Does the SR include failure rates for Opto-Electronic components?
Yes, it includes generic categories of single LED/LCD segments, photo-transistor and photo-diodes, single and dual isolator detectors and resistors, including light sensitive. Does SR-332 provide test requirements for testing an electronic module?
No, it does not, but it can perform the calculation of the predicted failure rate (MTBF) of your module. The SR is a method of predicting the failure rate or MTBF (mean-time-between-failure) of a module based on published prediction failure rates for individual components in an electronic module. Does the ARPP software use a Markov model?
No, the ARPP software does not solve Markov models for redundant systems. The ARPP calculates failure rates for a group of components in a series, which may then be used as input failure data to calculate the reliability of parallel redundant systems by mathematical equations. Is SR-332 an all-sufficient document, such as the MIL-HDBK-217?
Yes. However, SR-332 contains component failure rates for devices up through 2015, while the MIL standard contains failure rates for devices only up through 1996. Are the prediction procedures applicable for electronic boards used in medical applications?
Yes, SR-332 applies to all types of electronic circuit boards, even those used in medical applications. Are temperature and humidity conditions selectable?
Operating temperatures can be set to any temperature in degrees C. Humidity is not a parameter in this program because it is not as critical as temperature. Does the SR calculate the FIT for aluminum polymer capacitors?
No, this type of capacitor is a relatively new product device and was not available at time of issue. It will be addressed in a future update. How is the reliability for solenoids covered since they are not mentioned in the document?
SR-332 covers mostly electronic parts, whereas a solenoid contains both an electrical (coil) part and a mechanical (actuator) part. A better match would be for a Relay, which contains both an electrical coil and mechanical parts. For the software tool, can I select a component de-rating (like capacitors at 50%), and are temperature and humidity conditions selectable?
Every component (like capacitors) can be set to any electrical stress level from 1% to 100% and operating temperature set to any temperature in degrees C. Humidity is NOT a parameter in this program since it is not as critical as temperature. Does the ARPP allow for other methods of failure rate calculations such as laboratory and field data?
Yes. The ARPP allows for all three methods defined in SR-332. Does the user only have to input the component type and subcategory, and the spreadsheet automatically fills in the failure rate?
It is correct that the user only has to input the device category and subcategory for the spreadsheet to automatically fill-in the generic failure rate data. In some cases, the user must also provide a complexity (e.g., number of transistors) as well; the spreadsheet also automatically handles this case. What is meant by the component classification by type and subcategory being “linked internally” to the latest Telcordia failure rate predictions?
“Linked internally” refers to a worksheet in the workbook that contains generic failure rate data and to internal formulas for devices with a complexity value. There is no online link. The spreadsheet is self-contained. These all replicate the techniques in SR-332. Does the ARPP provide the capability to account for the various input parameters such as operating temperature and electrical stress?
Yes. The ARPP provides the capability to input parameters at the unit level and component level. The unit level allows the user to select the operating temperature, electrical stress, quality level, and environmental factors to apply to the unit and all of its components. However, the user may select a different operating temperature, electrical stress, and quality level for individual components based on actual operating conditions of the component. Are the Bill of Materials (BOMs) for the unit predictions in the same Excel workbook as the components database, or can they be in a separate workbook?
BOMs can be in any workbook. They are input to the tool by cutting and pasting the appropriate columns into the tool. How suitable is the ARPP to products that operate in ambient temperatures as low as 20°C?
Reliability predictions are very much dependent on operating temperature. Therefore, the ARPP tool allows you to enter the ambient temperature at the unit-level. It also allows you to enter a temperature rise on individual components (typically heat dissipating components). Any ambient temperature may be entered in degrees celcius. Can the ARPP be used for LED luminaires?
The ARPP tool is intended for predicting the failure rate of any electronic equipment based on environmental parameters such as temperature, electrical stress, and component quality level. It is widely used by industry for predicting the reliability of equipment from the simplest interface module to the most complex systems with many circuit boards. The ARPP contains individual component failure rates for all types of electronic parts, including LED devices. Does SR-332 contain failure data for Printed Circuit Boards (PCBs) or Printed Wiring Boards (PWBs)?
SR-332 does NOT count FIT rates for the bare PWB (or bare PCB) because the board itself is considered a passive connection. Therefore, it does not follow the time-to-failure model like components. And finally, a bad solder connection on a board is considered a workmanship problem rather than a reliability failure. If the Operating temperature is above 60°C, my interpretation of Section 9.1 is that I will need to manually change all temperature stress curves used to curve 7, irrespective of what curve was originally configured.
If the operating temperature is above 60°C, the tool will provide a warning, but calculate the proper temperature factor using the temperature curve that you have selected based on the device type. How can I incorporate the fact that I select industrial or military grade components instead of commercial grade? Surely this will have an effect on the MTBF calculation?
It is possible to specify a “quality factor” for each component. The default is II, which has a multiplicative factor of 1 and thus makes no difference. If a higher quality component is used, you can set the component to quality factor III, which will decrease the failure rate. If devices have lower quality, quality factors of 0 or I are used. Junction temperature of ICs ---- A factor should be added that increases the failure rate of an IC when the junction temperature starts approaching the maximum allowed junction temperature of the chip. Therefore, the failure rates of ICs would be both a function of their case temperatures and how close they are operating to their maximum allowed junction temperatures.
The generic failure rates used in SR-332 are based on device operating (case) temperature and not junction temperature. The temperature curve for an IC takes into account the effects of temperature on the device FIT rate. Also, it is recommended that the IC is properly derated to maintain a junction temperature margin of 20°C so that the device never approaches its maximum temperature. In the new issue of SR-332, are the failure rates of parts being changed? Are there updates to calculation methods, etc.?
- The majority of the device failure rates and calculation methods are not being changed.
- Some very small chip devices (i.e., film resistors and ceramic capacitors) will have lower FIT rates in Issue 4 due to recent field data, but the majority of devices such as ICs will not be changed.
- Several new devices are also being added such as Polymer capacitors and Organic capacitors.
- SR-332 and the ARPP software tool calculate the MTBF of a circuit board, module, or non-redundant (series) system by simply adding the predicted failure rates of the individual devices. This is often referred to as the “parts count method”. Once the circuit boards or module failure rates are calculated, it is up to the reliability engineer to determine which modules are critical that affect the entire system, and which modules are considered non-critical to the system operation. If the system contains redundancy, the engineer must calculate the system MTBF from reliability equations found in textbooks. SR-332 and the ARPP tool do not calculate results for redundancy, since there are many types of redundancy (i.e., 1+1, N+1, m+n, etc.).
- From the SR-332 predicted failure rate (MTBF) for each circuit card, you can add failure rates if the cards are in “series”. If the cards are in parallel, you must use a formula for that type of redundancy to calculate the equivalent MTBF for the redundant modules.
Yes, the software contains individual FIT rates for generic component categories and subcategories. These FIT rates are based on data provided by participating manufacturers during update meetings. Therefore, the SR-332 document and its accompanying ARPP software tool are one of a few reliability prediction standards that are continuously updated by participating members. What I am really looking for is commercially available RM&A data for electronic and mechanical components.
The SR-332 document and ARPP software tool provide generic component-level failure rates for all types of electron devices. From this document, failure rate predictions are calculated for printed circuit boards (PCBs) based on the sum of the individual electronic component parts modified by stress parameters for temperature and electrical stress. The SR-332 document or ARPP tool do not calculate a system's reliability, maintenance rate, or availability. These calculations require knowledge of the system architecture and redundancy. However, SR-332 does provide the basic PCB-level failure rate that is required in all RMA analysis. Is there anything publicly available that shows a sample device and what the predicted MTBF is in various issues of Telcordia – including Issue 4 – that we could use as an example? I’m mainly looking for a sample comparison of Issue 3 to Issue 4.
- Our reliability engineer did a comparison between Issue 3 and Issue 4 on an average circuit board and found that the new Issue 4 results are about a 14% reduction in the predicted failure rate.
- This comparison was done at “default” conditions of 40°C, 50% electrical stress, quality level II, and indoor environmental factor 1.0. Since the operating temperature, electrical stress, and quality level definitions and formulas have not changed, the same 14% reduction would also hold true for different model assumptions. One exception is the environmental factor for “moderate uncontrolled” outdoor environments, which was lowered in Issue 4 from the previous 1.5 to 1.2. This new environmental factor of 1.2 would further reduce the Issue 4 estimate for only outdoor (uncontrolled) environments.
- The reason why the reduction between Issues 3 and 4 is not as dramatic as between Issues 2 and 3 (about 40% reduction) is because the basic formulas for calculating IC failure rates remain the same in Issue 4 as in Issue 3. In fact, the same argument can be made for most other parts, including passive devices such as resistors and capacitors. The major changes in Issue 4 are to a subset of devices (such as electrolytic capacitors, connectors, some diodes) where field data showed a lower failure rate. Issue 4 also adds several new device subcategories (i.e., surge protectors, 100-Gbit optical transceivers, etc.) not previously covered by Issue 3, giving the user greater flexibility in choosing the correct device subcategory.
- SR-332, Issue 4 (with the ARPP software tool), is the most up-to-date reliability prediction procedure in the market today. It is used worldwide for predicting reliability for all types of electronic products and is recognized by industry as the most common referenced prediction method.
The Bipolar Digital Integrated Circuit Failure Rate formula definitely needs the minus sign. It seems the issue 3 was first published without it, and it was corrected a month later in Feb 2011. With the minus, the formula, table below it and tool all match and have reasonable FIT rates. I was first involved in the issue 4 update and did not realize this was changed in issue 3. The issue 2 rates seem fine, but were a bit higher than might be expected from evolving technologies. Without the minus sign, the formula returns failure rates much higher than in issue 2 which would not be expected. I have a question about the Telcordia SR-332 Issue 4 Connector model. On page 8-3, there's new text in Note b: "b. Failure rates are per contact pair." I'm confused: this new text seems to imply a big change for Connectors from previous versions of SR-332 (lower failure rate by factor of 2). This seems to imply that......failure rates given are for a mated pair of connectors ...failure rate for a single connector = 1/2 * failure rates given. Please clarify this for me.
The FIT rate for multipin connectors has been up and down in the last few issues. I don’t think the note appended to the table represents a change as much as a clarification as to how the rate should always have been applied. Since the connections are always a mated pair, the failures are likewise always in pairs. A failure is failure of a connection and does not count as two failures just because is includes both a pin and a socket. It is correct to apply the fit rate based on number of mated pairs, which is the number of active pins.
- The actual FIT rate was 0.1 in issue 2.
- It was reduced to 0.03 in issue 3.
- And was raised to 0.04 in issue 4. I cannot speak to the earlier changes, but the issue 4 change was based on lab measurements of connectors from one of the forum members who performed reliability tests in-house.
- Our experience is these types of non-power connectors are much more reliable than power connectors due to the lower currents and lower resistance heating. Also note the FIT rate assumes the connectors are made in accordance with the GR-1217 requirements. Lesser quality commercial connectors would be expected to have a higher failure rate.
- For all connectors, the failure rates apply to mated connector assemblies. For future issues of SR-332, in note b for connectors, we could possible add a sentence after the note that reads: "For "un-mated" connectors, or connectors to be mated in the field by the client, count 1/2 or 50% of the mated FIT rate value.
Per our statistics consultant: this distribution would be a Gamma distribution, with parameters 2 and ?. Suppose the FIT rate is random variable X. Then, X ~ Gamma (2, ?). Gammas are always defined by 2 parameters. In this case, the first parameter must be 2, but the second parameter can be anything, and the property where the standard deviation will be 0.707 times the mean will hold. This means that the std dev is (v2)/2 times the mean, which means that the variance is ½ times the mean squared. For the Gamma distribution described above, the mean is equal to 2/?, while the variance is equal to 2/?2. Is the variance equal to one half times the mean squared? Yes: 2/?2 = ½ * (4/?2) = ½ (2/?)2 = ½ (mean)2 I am sure that you could have any number of distributions where this property holds, but Gammas are very popular, and are related to the exponential distribution family. In fact, a Gamma (1, ?) is an exponential distribution. For SR-332 issue 03 and issue 04, is any Naval environment listed? Can you recommend a way for performing calculations for a Naval environment? Is there a conversion factor or something comparable for a Naval environment?
Naval applications were not addressed. I would expect it would be in between airborne, commercial (3x Factor) and space-based, commercial (15x Factor), but we have not done research to determine a suitable factor for naval applications. When entering a FIT number myself, from a part vendor for example, what column in the excel sheet should I use (I made a copy of the Unit Estimation tab)?
Telcordia suggest using the drop-down menu for Device Classification and Device Sub-classification and Complexity (For example: Connector, Multi-Pin, 8 pins). The FIT rates in the Telcordia ARPP tool are based on actual customer field data which typically tends to be higher than vendor data which is often based on limited accelerated life test (ALT) data which may not reflect the true field return failure rate. However, if it is necessary for you to enter a FIT rate from a vendor, you may enter the FIT rate in the column called "Mean Device Failure Rate" (column I). The FIT rate you add for this device will be automatically be added to the total unit failure rate in the upper half of the ARPP tool. Does this software tool import bill of material (BOM) from excel or design files? Manual typing?
The tool can’t determine component estimated reliability from a simple BOM. If you have a BOM in excel format, you can paste the device names and quantities into the tool. You will still need to identify the device category and device subcategory from the pull-down menus, and for some device types, enter a complexity value, for example, number of pins for multipin connector. This is how most users seem to use the tool. If you want to automate a bit further, you can assemble a database of your devices, with predetermined device categories, device subcategories and complexities in a format the tool can import. The database can be linked to the tool, and you can manually enter or paste columns of device names and quantities into the tool. From the database, based on the internal device name or code you assign it, it will retrieve the preassigned device category, device subcategory and complexity. Based on these, along with the quantity, the tool will calculate the estimated reliability. As I go through my unit and it’s bom, I come across parts that seem they would not normally fail. Like wires, iron beads or ferrite beads on wires, suitcase jumpers, individual pins and mating sockets… I know pcbs (or pwbs) are not considered for MTBF but what shall I do with these other items?
- Naval Wires: NO - do not count
- Ferrite Beads: YES, classification - Inductor/ Ferrite Beads
- Jumpers: NO (but some uses have classified jumper wires as - Connector / Multi-pin, 2 pins)
- Mating Socket: Yes, All mating connectors on a board are classified as Connector / Milti-pin and # of pins. However, the FIT rate for an IC socket already includes its pins plus the pins of its mating socket, since connections are counted as a "mating pair". So it is not necessary to count IC sockets if used on a circuit board. Today ICs are mostly surface mounted eliminating the IC socket.
We agree. Ignore those items. What should we use in the ARPP to cover sockets (not IC sockets you mentioned below), 40 mil sockets for example, that are inserted into a pcb with purpose to accept 40 mil pin as a one-time connection (for example a daughter pcb inserted into a mother pcb, using 40 mil pins into 40 mil sockets).
The second part I think I would treat as a connector, multi-pin. Connectors on boards are to be counted. These are mostly multi-pin connector with the number of pins entered into the ARPP. Also connectors used on the board for 120/240VAC or -48VDC, are classified as Power Connectors, and connectors for radio frequencies are classified as Coaxial Connectors. I’ve run across a question on what to do with small smd RF amplifiers. It’s described as a monolithic amplifier. It’s not what I consider power amplification, it can be used in cell phones for example. How to come up with the failure rate using the ARPP tool for SR-332?
I would consider this a Transistor > Amplifier, Power, RF, InGaP/GaAS/SGs HBT. Mean FIT or 3.2 In SR-332 issue 03, Table 8-27, I have a question about the FIT value of the Quartz Crystal? According to the standard, the Lambda value is 3.2 but Sigma is greater than Lambda in this case.
Those are the issue 3 numbers, and were not updated since issue 2. They were updated in issue 4 with a much lower std deviation. I was not directly involved in issue 2, and don’t have anything on my pc that goes back that far, but would agree that there was either limited data or a lot of variability that resulted in the high std deviation. For issue 4, there was data from ALU and IDirect which was combined to give better estimate. I´m working with the Standard SR-332, Issue 3 and I`m working also with the calculation tool. I detect a mismatch between the Units of the capacitor values. In you Excel file you write mF and in you standard you use µF. Which unit is the right one?
All units are micro Farads. We will revise the tool units in the next edit. I chose to use your issue 4 spreadsheet to do a couple of predictions and noticed that the failure rate of a component only goes as low as 30C. Can you explain why the calculation only goes down to 30C? I have an application where I will be using my product down at 0C, 8C and 18C, What’s the spreadsheet is showing me is that temperature make no difference with respect to failure rate at lower temperatures.
The SR addresses the concerns of increased temperatures above normal design and uses an Arrenihus model to predict the impact of higher temperature on reaction rates. In theory, lower temperatures would have a reduced reaction rate and an increased reliability, assuming other failure mechanisms are not introduced. Why don’t you extrapolate the curves down, calculate the reliability, take that as a first order approximation (maybe with an adjustment for any unknown new failure mechanisms), and refine it going forward with field data. When you say actual customer field data, is there a number of field hours (say 100 / 200 million hours etc.) that you are considering for the component FIT rates in the Telcordia tool?
The data used to update the SR-332 FIT rates comes from SR-332 participating members of the telecom industry. These members collect failure date from many systems over a long period of time, This data typically represents billions of unit-hours of operation. From this data, FIT rates and standard deviation are calculated.
In the Excel ARPP software can you change the Confidence Levels? I need to change the CL from 90% to 60%, etc.
Yes. The tool has a selection for Upper Confidence Level. The user can pick a UCL between 50 and 100% and the tool will return the UCL FIT rates for Early Life and Steady-State Failures based on the chosen value.
Updated Jan 25, 2024