Strategies for Components Documentation

When a manufacturer offers a product for sale, the design engineers expect to have access to documentation that provides sufficient information to determine whether the product will perform as needed for the design under consideration. This is a fundamental requirement for electronic component parts and assemblies.

For components that are intended for use in assemblies, the manufacturer will not only furnish a datasheet covering the essential parameters of the part, but may also include an "Application Note" directly within the datasheet. This is usually in the form of a practical clarification of some aspect of the component, coupled with small block diagrams or schematics.

However, for more sophisticated parts, the Application Notes may exist as separate and more comprehensive documents. For a typical semiconductor datasheet, Texas Instruments Inc. (NYSE: TXN) has published a paper titled "How to Read Datasheets" by C.J. Ganier. The paper is fairly comprehensive; if you would like to become more familiar with datasheet terminology, this is an excellent introduction. Here is the intro of the Abstract:

For every electronic component or series of components, the manufacturer or designer produces a datasheet. In its early stages, a datasheet might be the specifications the designer works from; but, by the time the device is released, the datasheet is the essential piece of information that describes exactly what the component does. Everything from the smallest resistor to the most elaborate processor needs a datasheet.

Datasheets focus on electrical properties and the pin functions of the device; usually the inner workings of the device are not discussed. This is partly to make industrial espionage more difficult, and also because the user should not need to know the internal workings of the device. In practice, if you find that you need to know how a particular product works internally, you can often call the manufacturer and find what you need to know.

For most documentation, the following is covered in great detail:

• Manufacturer's part numbers and associated options specific to unique characteristic variations of the part. These are usually found in a section labeled "Ordering Information." The main part number is usually at the top of the first page in a large, bold text.
• The part description
• A picture or line drawing of the part
• The introductory general feature information
• The package or form with dimensions
• Pin-out diagrams
• Tables for function and operating characteristics (usually specified as "Min," "Typ," or "Max"). Values, including, but not limited to:
1. Temperature
2. Voltage
3. Power
4. Power dissipation
5. Current
6. Impedance
7. Frequency
8. Timing
9. Value
10. Tolerance
11. Package -- form factor options with part number ordering information
12. Package thermal characteristics
13. Gain (for transistors)
14. Switching speed
15. Humidity or other Environmental limits
• Additional drawings showing footprints, land patterns, or hole cutout specifications
• Materials used to make the part if required by law
• Charts showing various performance characteristics on a two-axis plot format

Component documentation should be quickly accessible via a part management system that is either 1) based upon a software database application that links "attachments" to part numbers; and/or 2) a hard-copy set of files storing all relevant documentation associated with the component or assembly part number. Refer to the core-disciplines tab at www.componentsengineering.com/core-discplines for more detailed information on this and related engineering subjects.

It is of the utmost importance to refer to the manufacturer's datasheets when qualifying a part to determine if the part performs as stated. Having the datasheet will also help with designing the qualifying test procedure unique to the component or component family type. Recently, Silicon Expert released a Web-based search engine that has datasheet information on more than 180 million parts. This engine can be found at www.datasheets.com or at other various (hosting) Websites, including www.ebnonline.com and www.componentsengineering.com. Datasheets.com also has inventory counts and costs at the various participating distributors. It is an excellent source for part availability searches in general.

Purchasing must also have access to the component data information but may not require the full set of datasheets. This is why the component engineer creates a Purchasing Specification Document (PSD) or a Specification Control Drawing/Document (SCD). This is an abbreviated form of the full specification citing the critical parameters of the part and usually incorporating a drawing of the part with dimensions, if applicable.

Many times, a vendor will take advantage of a purchasing agent's emergency part purchase requirement and suggest an alternate part that is not a true parametric substitute. The purchasing agent is bound to the PSD and is not allowed to purchase a substitute part that is not on the PSD or SCD. The purchasing agent may send non-proprietary PSDs to a vendor to help the vendor better match the original component, but the component can only be purchased after it has been added to the Part Master's approved vendors list by the component engineer or when a sustaining or design engineer has signed off on a temporary manufacturing deviation, thereby allowing the use of the substitute part only until the original manufacturer’s part number can be sourced.

This is the best way to avoid production problems due to underperforming or non-performing part substitutions. PSDs and SCDs must also be under revision control. A PSD form template is downloadable here.

Having all the datasheets available either in hard copy or in PDF soft copy with links is the best practice for rapid retrieval of critical part information. These datasheet files should be part of the overall project file created for the product during the R&D phase.