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Old 17th November 2006, 04:32 AM   #1
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Default Ceramic caps: SMT as good as radial?

For bypass applications, are SMT caps (0805, 1206) as good as radial, all else being equal?
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Old 17th November 2006, 05:04 AM   #2
suzyj is offline suzyj  Australia-Aboriginal
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They're much better, as the lead inductance is considerably lower.

Much the same goes for resistors (chip resistors being better than leaded ones). The best resistors I've used are Melfs. They're barrel shaped, with metalised end caps. You can get ones to fit a 1206 or 0805 footprint, so they're interchangeable with normal chip resistors.

Cornell Dubilier mica chip caps are also very cool. They come in 0805, 1210, and 1812 varieties, in values from 5p to 1n or so. As with chip ceramics, the lead inductance is lower, so their SRF is correspondingly higher.

I try to use SMD parts wherever possible with my designs. They're more compact, more robust, electrically better, and I find them easier to build with than leaded components.

Regards,

Suzy
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Old 17th November 2006, 12:24 PM   #3
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Quote:
Originally posted by suzyj
...I try to use SMD parts wherever possible ... I find them easier to build with than leaded components.

Regards,

Suzy
Just wait until you reach 40+ years old Suzy. SMD won't be so easy to use then
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Old 17th November 2006, 12:48 PM   #4
djQUAN is offline djQUAN  Philippines
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Quote:
Originally posted by BobEllis


Just wait until you reach 40+ years old Suzy. SMD won't be so easy to use then

I agree with suzy. And I still have 18 years to go before knowing what Bob is talking about.
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Old 17th November 2006, 06:38 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
I past Bob's problem 16years ago and now regret buying the round MELF (diodes) instead of the square ended (only one digit error in the order number) I thought I was buying.

SMDs are much slower to place and generally of lower voltage than the leaded parts.
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Old 17th November 2006, 06:50 PM   #6
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Quote:
Originally posted by BobEllis


Just wait until you reach 40+ years old Suzy. SMD won't be so easy to use then

I use a pair of tweezers and a loupe !!! If you use solder paste the devices will "kinda" stick to the solder paste and not jiggle around.

Not good after 4 cups of coffee, or a couple Red Bulls however.
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Old 17th November 2006, 09:39 PM   #7
suzyj is offline suzyj  Australia-Aboriginal
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I'm getting pretty close to 40, and do find things aren't as easy to see as they were in my 20s. However big parts like Melfs aren't hard to place at all. A good magnifying lamp is useful. I've got a Luxo one on my bench at work that's great for everything down to 0603 or so. If it's smaller than that (0402), I use a microscope. I have no magnification at home, but generally don't do stuff smaller than 1206 odd at home anyway.

The technique is the key to getting good results. I start by putting a healthy dot of RMA flux on each pad. Then I apply a small amount of solder to one pad (with about a 1.2mm soldering iron tip). I reflow this solder while I hold the component in place with tweezers, then finish by applying some solder to the other end.

The key is the flux. You really can't have too much. I use RMA because it's _much_ easier to clean off than noclean flux, which is supposed to be left on the board. Once I'm done soldering, I just scrub the board in some safewash, then rinse with distilled water.

It's also good to find the smallest diameter solder you can, as it's very easy to use too much solder, especially with 0603 and 0402 parts.

Cheers,

Suzy
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Old 17th November 2006, 10:12 PM   #8
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I stick with leaded parts at home when possible. I do electronics at home for fun and edification, not self-torture. The leaded assemblies are a lot easier to troubleshoot and adjust. Besides, have you ever tried matching and sorting SOT-23 JFETs? I'll take the old TO-92 parts any day.

At work, I have to deal with SMT parts as a matter of course. A good pair of tweezers (non-magnetic!), a clean fine-tip soldering iron, and an illuminated magnifier are musts. I also tin all the pads before I start assembly, as it makes placing parts much easier. We don't do enough volume to justify having solder paste around.
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Old 17th November 2006, 11:40 PM   #9
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I have been working as an embedded systems engineer for a few weeks now (fresh out of school, and learning a lot more now than I ever did then). I was totally freaked out by SMT parts at first, but now 0805 and SOIC parts are easy. I have a little trouble with SSOP but after having done ~4 of them, I can usually get one soldered down with only having to fix 1-2 pin bridges. Flux helps a lot on the SSOP's but I now don't even have to use any in addition to what's in the solder.

Anyway, back to SMT parts quality - what about resistors? I know 1% axial metal films are the de facto standard in the audio world. What are the best/good SMT parts? Thick film, thin film, metal film, etc? I don't know what to use.

PS - it is nice having a job like this, my hobbies are going to get significantly more awesome with the experience I am getting.
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Old 18th November 2006, 01:11 AM   #10
Leolabs is offline Leolabs  Malaysia
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SSOPs are easy to deal with.QFP is a little bit tricky,esp the ones with more than 200 pins.,solder with normal 25W iron.
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