Author Topic: SMD resistor with marking  (Read 594 times)

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Offline tszabooTopic starter

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SMD resistor with marking
« on: May 27, 2024, 08:51:23 am »
I design PCBs that get used in ATEX/IECEx electronics, and are intrinsically safe. It means that the electronics could go into areas where there are gasses in the air that are combustible. The electronics therefore have to fulfill a lot of requirements.

Here is my trouble: I was using a resistor provider, that over the past 2 years silently removed all markings from their resistors. Even the large, 2512 parts don't have marking on them anymore. To make matters worse, I use the regular and the high power variant of the same series, and there is zero way of telling them apart. This is an issue, because visual inspection of the board no longer makes it possible to identify a wrongly placed part. Some of these resistors provide safety to the electronics, so having the wrong part could mean dangerous situations or recalls.
And measuring is not possible after conformally coating the electronics.

I would like to switch to a provider that is:
-made by a reliable supplier
-provides highly reliable parts
-have good documentation
-and has markings on their part
-comes in reels
-doesn't cost an arm and a leg.
Their portfolio should also be "complete" meaning E192 from 0 Ohm to Megaohm, and all parts from 0402, 0603,0805 2010 and 2512, and usually stocked. 0402 might be without marking.

Any recommendation?
« Last Edit: May 27, 2024, 08:53:15 am by tszaboo »
 

Offline temperance

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Re: SMD resistor with marking
« Reply #1 on: May 27, 2024, 11:05:04 am »
Quote
Any recommendation?

We use a flying probe tester in our production line and test points for each component.

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I use the regular and the high power variant of the same series
Does the printing on a the high power variant look different? Just asking because I've never seen any difference.
 

Offline tszabooTopic starter

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Re: SMD resistor with marking
« Reply #2 on: May 27, 2024, 11:24:11 am »
Quote
Any recommendation?

We use a flying probe tester in our production line and test points for each component.

We do a combination of AIO, flying probe at the the assembly house, visual inspection and ICT at our site.
Unfortunately you cannot measure ~100KOhm resistors in circuit reliably, so imagine a resistor adjustable voltage clamp is already something that could be very problematic. And there is the issue that an automated machine with incorrect settings might let everything through. Visual inspection is important, it catched nonconforming PCBAs before, and our ICT doesn't provide 100% coverage.

Does the printing on a the high power variant look different? Just asking because I've never seen any difference.
The CRCW-HP has double sided resistive element for the high power versions, so it's visually different, but I cannot tell them apart unless they are next to each other.

 

Offline exmadscientist

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Re: SMD resistor with marking
« Reply #3 on: May 28, 2024, 10:40:43 am »
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silently
To their credit, they did issue a PCN about this. I promptly dropped them as a supplier when I received that PCN, so I know it happened....

KOA's RK73B RK73H series meets your need, except that E96 in 0603 it is not marked. (I also don't know if they offer E192, because in general E192 is so badly stocked that I simply never use it. I don't know that anyone really offers it.) They have the added advantage that they are blue, which means you can tell immediately if someone swapped out one of your parts without telling you. No one marks 0402s -- no one -- but their 0402 jumpers at least are green, which is very nice. They also offer red (red! so distinguishable!) surge rated parts, which are nice but a little pricey for what they are. These are my favorites because they are so easy to recognize.

Yageo is also excellent and very widely stocked. Stackpole is very good but historically not as well stocked. Both are well marked at 0603 (even E96) and above and describe their markings, either in documentation (Yageo) or on their ordering site (Stackpole). I will usually buy KOA for most parts then fill in with these guys.

Susumu is nice for thin films as their markings are distinctive to the company. However, they don't describe what they will and won't mark. I recall they didn't mark at least one thing I was expecting to have marked, but that might have been an oddball. They do mark 0603 in E24 and E96 and 0805 and up fully.

There are other vendors (TE isn't half bad, especially for high power stuff; you'd do well to look at CRGP and friends, E24 at least is fully marked in my experience), but as someone who also looks for markings (probably for a different reason... I am always working with prototypes that might come out wrong or get reworked, and markings have saved my ass more than once), these are my go-tos.
« Last Edit: May 28, 2024, 07:57:50 pm by exmadscientist »
 

Offline tszabooTopic starter

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Re: SMD resistor with marking
« Reply #4 on: May 28, 2024, 05:57:17 pm »
Quote
silently
To their credit, they did issue a PCN about this. I promptly dropped them as a supplier when I received that PCN, so I know it happened....
I don't think I would be subscribed to resistor PCNs  :-DD
But yes, now I see they did. I don't get why they are not keeping their marking on the CRCW, and loosing it on the CRCW..C which is the standard version of it. Why change such a fundamental part?
And I even had a meeting with a Vishay representative not that long ago, who told me to use smaller resistors because they get more parts out of one substrate, so they are cheaper... It was nice to just have the entire series in my Altium, and not to worry about the parts at all when designing, but that's over apparently.

The RK73B normally has 5% tolerance, that is not something I would entertain. But I see it has also 1% variants, that are 0.8 cents in a reel for 0603, and 1 cent for a 1206. Which is certainly OK.
I know of the supplier that you mentioned below, they sometimes make it into the designs, when specialty resistors are needed.
I think I'll talk to our EMS, maybe they stock some parts by default. And give KOA a second look tomorrow, sometimes I need application notes or measurements by companies to prove the safety of my designs. Vishay was excellent in that regard.
 

Offline exmadscientist

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Re: SMD resistor with marking
« Reply #5 on: May 28, 2024, 07:57:19 pm »
Why change such a fundamental part?
The official reason was AOI equipment. But you and I know the real reason....

Killing off 1206s is crazy :-DD I bet they're just trying to push their MELF line, which is much wider than other vendors'. 1206 might go up in price but it is not going anywhere!

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It was nice to just have the entire series in my Altium, and not to worry about the parts at all when designing, but that's over apparently.
If those are your priorities then I'd go with Yageo. They make everything, stock everything, and are sold everywhere. They did try to kill markings once but backtracked quickly... I don't know what that means for the future.

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The RK73B normally has 5% tolerance, that is not something I would entertain. But I see it has also 1% variants, that are 0.8 cents in a reel for 0603, and 1 cent for a 1206. Which is certainly OK.
Yes, I wrote too quickly. I meant to say the RK73H 1% series. Their 5% guys are nothing special, not that I even buy 5% ordinary resistors anymore.
 

Offline temperance

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Re: SMD resistor with marking
« Reply #6 on: May 28, 2024, 09:57:34 pm »
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The official reason was AOI equipment. But you and I know the real reason....

I've noticed that the carrier tapes also changed for some major brands like Yageo. They are now much thinner.
 

Offline tszabooTopic starter

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Re: SMD resistor with marking
« Reply #7 on: May 29, 2024, 10:03:01 am »
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It was nice to just have the entire series in my Altium, and not to worry about the parts at all when designing, but that's over apparently.
If those are your priorities then I'd go with Yageo. They make everything, stock everything, and are sold everywhere. They did try to kill markings once but backtracked quickly... I don't know what that means for the future.
The board house also wrote back that the other brand they stock is Yageo.

Quote
The official reason was AOI equipment. But you and I know the real reason....

I've noticed that the carrier tapes also changed for some major brands like Yageo. They are now much thinner.
You know we are saving the polar bears here, one milligram at a time. I have the warm and fuzzy feeling that todays planned obsolescence electronics with non-replaceable battery, software crippling and enshittification uses less paper, that gets recycled anyway.
 


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