Electronic – How to identify SMD components? (or how to identify any component)


How do I identify the markings on an SMT component and match it up with a part number so I can be a good designer and actually look at a datasheet (and read the whole thing)?

Or identify a part to replace an unknown part on a PCB?

Best Answer

Step 1) Identify the package, note how many pins, match up the pins first. Note that sometimes the package pins are underneath the part or extended away from the part. Also get the dimensions of the part with a ruler or (preferably) calipers and match them up with a chart, write them down for a later step. Make sure that when measuring pin pitches (distance between pins) that this is done accurately, it can be difficult to tell (for example) the difference between a 1mm pitch to a 1.25mm pitch. Make sure the measurement is precise, or measure across multiple pins and divide by the number of pins to get the pin pitch.

Package dimensions are standardized IPC-7351 or they can also be found by searching for the package type on google and comparing dimensions. Package dimensions can also be found at manufactures websites in datasheets (or sometimes in files separate from datasheets, it might take some hunting around to find them)

Here are some resources to help you find different packages or use this below:

enter image description here Source: NXP

Step 2) Identify all markings on the top of the component. These markings include: Manufacturer Logo and\or SMT code.

If you are unsure of character differences, make sure these are noted. E.g.: 8 could be mistaken for B. That means if you have A32B it could be mistaken for A328. If you're unsure, you will need to search for both. Here are some sources where you can find them:

You can find many IC manufacturer logo's using this link or the picture below:

enter image description here Source: Electronicspoint

Step still can't find it 3) So what do you do at this point if you can't find what your part is? There are still lots of options. Use what you know about the part.

A manufacture logo or mark on the package can be really helpfull to identify the package. Use parametric searches at the manufacturer's website and package information to narrow down the number of parts. For example: if I thought the part was an opamp with 5 pins and I knew the manufacturer was TI, I would go to TI's website and run a parametric search that looks for all of the opamps with 5 pin packages.

Then start checking datasheets as most of the leading manufactures provide SMT codes in datasheets with the package information. If it is an old part, a search through old datasheets or maybe an email to the manufacturer might be the way to clarify the part. Many manufacturers have also SMD code lists.

The more certainty you have of the package type (or narrowed it down to a few packages) and you think you know what the part does, you can use a distributor search (such as Digikey, Mouser, or Octopart) to narrow down what the part is. This allows you to pull up a datasheet and check.

I have also found extremely vague parts on google just by the package and the SMD number. I tried different combinations of packages (I had two choices), and after some google sleuthing, I narrowed it down to 3 parts. With some testing, I found my part.

If all that doesn't work, and your part is still functional, you might have to do more reverse engineering of the circuit and find the functionality of the part.

For example, if you know its a transistor, you could verify the type of transistor with a multi meter or diodes can be easily determined with the diode mode of a meter.

Because of current leakage in a circuit when it is off, parts such as capacitors or unmarked resistors may need to be desoldered from the board to find the true value (the rest of the circuit is in parallel with the component when the terminals of the meter are placed across it).