Parts is parts - Page 1
Forum section: electronics / general

author: PbFoot
author_rank: Contributor
timestamp: November 09, 2012, 09:57:38 pm
content: Hi,We've all seen what cheap electrolytic caps will do, and what brands are decent. This leads me to wonder about other types of parts. Setting aside outright counterfeit parts, do I care if my 74 or 4000 series IC is made by Motorola, TI, Fairchild or ON Semi? Same for other semiconductors. What about resistors? Often I don't even know what make they are.With some types of parts are they all basically the same quality? LEDs? Relays?-PbFoot

author: poptones
author_rank: Frequent Contributor
timestamp: November 09, 2012, 10:10:04 pm
content: It's not universally true, but lots of stuff you will find digikey is the same price or even lower than ebay wonhunglo prices, and you don't have to worry about getting bad parts from them.Here's an example: I bought some 1n4007 rectifiers from parts plus. They're standard 1A parts you'll find at radio shack with what appear to be about 13ga leads. I bought 1000 of them from wonhunglo at a fraction of a penny each and the bodies are considerably smaller and the leads appear to be about 16ga wire. Now these are for experimenting and so not at all critical, but if you were actually building something, like maybe a HV step up convertor, you might find that the chinese parts, while tolerating the spec voltage, burn up at about 100mA or overheat with regular use.Resistors are often the same way: what are specd as quarter watt leaded parts may only really be 1/10 watt. When they're less than a penny each in 1000 quantity, why skimp?I ordered some 74hc595s from china, I thought I got them at a good price (about twenty bucks a hundred). Same with TL072s. Turns out I can get the same part numbers, and not have to worry about quality, at a lower price from digikey.Like I said it's not always true and a lot of the stuff you buy is from there anyway, but don't assume a deal is a deal. I often buy surplus, that's often a deal and an omron led is an omron led.

author: Neilm
author_rank: Super Contributor
timestamp: November 09, 2012, 10:17:34 pm
content: Quote from: PbFoot on November 09, 2012, 09:57:38 pmLEDs are very variable. Good quality ones will meet there spec for longer. If you are designing for commercial products, the last thing a good designer would want would be for the LED to get so dim it can't be seen.Likewise with relays. At work we have two almost identical relays in the stores. One is twice the price of the other. The reason, when it is closed it has only 2 mohm of resistance where as the cheaper one can be anything up to 100 mohm. There are applications where this difference can be come significant.Semiconductors from different manufacturers can have slightly different performances. Not usually in the headline specs but something deep in the datasheet. I have had to debug a system where the production run had been good for many years, then all of a sudden we had over 90% failures. It turned out that the system could not use chips from a particular manufacturer (it was noted on the schematic that this was so). Purchasing had decided to buy the chips as they were cheaper not realising that it was not on the approved list for that part number.NeilNeil

author: David_AVD
author_rank: Super Contributor
timestamp: November 09, 2012, 10:19:42 pm
content: Sometimes there are subtle differences between manufacturers of a particular IC. Whether that affects you will vary case by case.For example, I recall many years ago that some versions of one CMOS chip were rated to 15V while another was 20V.

author: poptones
author_rank: Frequent Contributor
timestamp: November 10, 2012, 01:08:36 am
content: I had that bite me in the butt once too. We were using a DAC0808 in a product and bought some Motorola parts and all of a sudden the board didn't work. Turns out the Motorola version would not allow a vref hgher than VCC. Most parts didn't care, the Motorola did.

author: necroscope
author_rank: Regular Contributor
timestamp: November 10, 2012, 07:02:19 am
content: Quote from: PbFoot on November 09, 2012, 09:57:38 pmfujitsu TTL's seem to be the worst offenders on a lot of 20year old pcb's i work on especially the fujitsu 74LS157 or 74LS245 seem to be the most common with a high failure rate.

author: nctnico
author_rank: Super Contributor
timestamp: November 10, 2012, 10:56:14 am
content: I've had a lot of bad experiences with chips from Sipex. In one particular project there was a 100% failure rate on a watchdog chip.

author: rsjsouza
author_rank: Super Contributor
timestamp: November 10, 2012, 10:29:38 pm
content: In the 70 and 80's there was a large variation between ICs and transistors from the same manufacturer depending on the country that performed the final assembly of the devices.These variations were mostly caused by the material of the lead frame, the internal gold wiring and the process used in the assembly/test facilities (the places that receive the wafers from a fab and perform the cutting, mounting, soldering and packaging of devices).Given the actual scenario, I wouldn't be surprised this happens today with the less reputable manufacturers.Just to illustrate some recent experiences: one BA1404 (FM transmitter IC) and a few NTE transistors have terribly oxidized lead frames that could be caused by poor materials used on the lead frame. Although storage conditions could also contribute to that, I have 30 year old transistors and ICs that are in much better shape.

author: Wartex
author_rank: Frequent Contributor
timestamp: November 10, 2012, 11:49:37 pm
content: How is this topic relevant to Buy/Sell?

author: mianchen
author_rank: Regular Contributor
timestamp: November 12, 2012, 12:27:33 am
content: I bought about 100x blue LEDs from eBay for £10. Look at the result!... bought another 100 from Farnell, they look much better and only costs £12 + VAT....