Sourcing electronic components (SMD) from Ebay/AliExpress


  • Hero Member

    I was wondering what the deal is with all these cheap (reel SMDs) inductors, resistors, capacitors etc that can be found on AliExpress (and sometimes Ebay). Is there a downside to them? I have googled quite a bit but found no real reviews or suggestions regarding the topic. Are they considered knockoffs / generics in general? Does it matter? Is there a catch? Any class of component that one should absolutely avoid?

    Half the problem of getting anything done seems to be sourcing components ... seems you can save a fortune on some of these bread-and-butter components compared to buying them from Mouser / Digikey / Elfa etc.


  • Mod

    From my own experience you can get good stuff from AliExpress but beware.
    When you look closely on how for instance make and model are described you will find out that the real cheap ones don't mention a make or the model is 'custom' (or whatever they make of it).
    That is the point were I skip the seller.

    I have seen this quite a lot with the ATmega...


  • Hero Member

    @marceltrapman Yeah, that is the deal with virtually all SMD reels I've seen. They're completely generic. No brand. No nothing. Not even a description most of the time.

    But sure, it is tedious to enter information for a gazillion different resistors so I guess that could explain the lapse.

    To put this whole question another way. Does branding matter when it comes to bread-and-butter smd components?


  • Hero Member

    Having actually done some reading for once, I now realize that these cheap capacitors at least are mostly un-rated and have terrible variance. But perhaps we can live with that?

    Also, some questions about life-span remain. Turned out to be a more complex situation than I had anticipated.


  • Hero Member

    Especially with capacitors be careful about life-span.


  • Admin

    I buy my SMD components from reputable places like Element14 or Digi-Key. Parts arrive in antistatic, anti-humidity, vacuum-sealed bags to avoid problems if you assemble them using a reflow oven.


  • Hero Member

    @daulagari Yep, turns out to be a factor even with ceramic capacitors. So to anyone else looking for cheap caps, don't buy unrated if you can help it. You'll most likely get specs that are less than the lowest rated models:
    http://en.wikipedia.org/wiki/Ceramic_capacitor#Class_2_ceramic_capacitors
    http://www.powerguru.org/dielectric-performance-of-ceramic-capacitors/
    So that would be less than both Y5V (−30/+85 °C, ΔC/C0 = +22/−82%) and Z5U (+10/+85 °C, ΔC/C0 = +22/−56%) with an aging rate (capacitance drop) of 6% per decade or worse.
    Paraphrasing from the article above that would mean:

    1. 6% between 1 and 10 hours
    1. An additional 6% between the following 10 and 100 hours
    2. An additional 6% between the following 100 and 1000 hours
    3. An additional 6% between the following 1,000 and 10,000 hours, etc.

    If I've understood this correctly?

    Still, there may be relatively cheap rated caps available, but they are never part of these kits they sell, and not nearly as many values to choose from. Currently going through AliExpress rating by rating, starting at X7R, footprint 0805 ....

    @blacey I've been looking at some of these places, but there is always something off about them. Either the parts prices are sky high, or the shipping fees (including Swedish tax/custom fee/handling) are just crazy. Particularly the handling fee can kill these small orders, whether it be the Swedish Post or FedEx/DHL whatever. Tax/customs fee is a much lesser concern. The upside of AliExpress/Ebay for me isn't primarily that it is cheap, it's that the packages are always fraudulently declared, with no paperwork inside the bag, thus overwhelm the Swedish Post who are in the end forced to let the majority of them pass even though they are legally within their right to hold every one for further inquiry. But I digress, the point is that ordering components may be a lot easier depending on where you live and how much you order (seeing as many of these resellers offer some sort of free shipping option on larger orders). I'd have to combine an order with some of my countrymen on the forum at the very least for it to make any kind of sense.

    On a side note, got an email this morning from TI saying they will henceforth require a valid university / business email for ordering component samples.


  • Hero Member

    I have some 50pcs sample 1206 10uF ceramic caps that I got from AliExpress the other day. Purported to be X7R. I measured them (7 of them at least, it's tiresome to pick them up with pincers from the reel and put them back) with my DMM and they all checked in at between 9.5 and 10.1 uF or so. After having soldered two of them for prototyping, and heated them somewhat obviously, they measured at about 10.5 uF so not much of a change either. Is this information enough to say that the rating for these caps is good enough? Can't prove that is is X7R or whatever I mean, but that they at least can't be bottom of the barrel so to speak ...


 

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