Q: Are 0805 SMDs too big, too small, or just right? - Page 1
Forum section: electronics / projects

author: TheRuler8510
author_rank: Regular Contributor
timestamp: July 05, 2014, 01:00:47 am
content: Q: Are 0805 SMDs too big, too small, or just right for thehome reflow oven newbie?How about discreet semiconductors...are SOT-23 the best choice?Any other guidelines are welcome.Thanks in advance,Tom

author: mariush
author_rank: Super Contributor
timestamp: July 05, 2014, 01:11:55 am
content: I worked very little with SMD parts but considering 0805 parts are easy to solder by hand, they'd be no problem to solder using reflow (hot air gun, oven etc doesn't matter).I'd say even 0603 shouldn't be a problem, many people have no problems doing it by hand, a few may choose to use a magnifying glass.Won't say anything about your second question.. too little experience with smd parts like I said.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: July 05, 2014, 01:59:36 am
content: I would say SM0805 just right for starting out.Discrete SOT-23 are very easy for soldering.I use SM0805 as a default resistor size and 0603 for capacitors. Works for me. But obviously use different sizes when required.For MCUs and other ICs the qfp32s are very easy as are the SOICs.Once you change to smd you want go back.The next step, with a bit of practice 0.5mm pin pitch is fairly easy by hand. eg. qfp64.For the reflow I use an electric frying pan and a hot air gun in case of any cold spots. This is because I haven't been using stencils so my reflows tend to need fixing anyway.

author: TheRuler8510
author_rank: Regular Contributor
timestamp: July 05, 2014, 02:13:29 am
content: Quote from: HackedFridgeMagnet on July 05, 2014, 01:59:36 amThanks for the comments. Why don't you use stencils? OSHstencils is cheap. I have not used them yet, but soon I will try them.Regards,

author: Psi
author_rank: Super Contributor
timestamp: July 05, 2014, 02:16:23 am
content: yeah, 0805 are good for starting out with SMT soldering.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 05, 2014, 02:37:18 am
content: Quote from: TheRuler8510 on July 05, 2014, 01:00:47 amI dunno,Goldilocks---I'll ask the Bears!

author: SirNick
author_rank: Frequent Contributor
timestamp: July 08, 2014, 10:18:02 pm
content: Just started doing SMD myself. I use 0805 for resistors (1/8W) and caps under 10uF. Some datasheets I've read, particularly for finer pitch parts, recommend 0603 for decoupling, which would help keep them close and not take up space needed to pass traces around them. I'll probably move to 0603 caps once I get my sea legs.Working with them isn't so hard. I hand-soldered a little DIY SOIC-to-DIP adapter for an LPC812. It had one decoupling cap and two pull-up resistors. Not pretty, but it seems to have worked out OK. I drag-soldered the IC, and needed to use a little wick to undo some bridges. NBD. I just tried it by hand on a whim, and to my surprise, it wasn't as much trouble as I was expecting. Good tweezers and light are essential.I also have a hot-air station, which is magical. I'm still working out how much paste to apply. I usually end up with too much. The stuff I've soldered so far is all too simple (just a couple dozen components, tops) to bother with a stencil, but I have a project coming up where it will be essential. Hoping to have the hacked toaster oven ready in time for that one also. No idea what the thermal characteristics of a wand held at arbitrary distance, and set for 350C, is actually like at the board level.If I may thread-jack just a bit: Anyone have any tips (NPI) for cleaning removable solder paste nozzles after each use? Stuff's too thick to wash out in the tap, and the business end is too small to get much into them for scrubbing. I end up using small signal diode legs to poke and prod. Pretty tedious work.

author: poorchava
author_rank: Super Contributor
timestamp: July 09, 2014, 05:49:30 am
content: empty syringe does that for me.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: July 09, 2014, 05:53:21 am
content: 0805 = Hand soldered board, power components, things that need frequent servicing0603 = Reflow board, occasionally hand-serviced0402 = Reflow board, rarely hand-serviced0201 = Mass production mobile device, no servicing at all01005 = Fuck me

author: Dago
author_rank: Frequent Contributor
timestamp: July 09, 2014, 07:21:47 am
content: I've been using 0603 as my standard SMD passives because 0805 are quite big compared to high pitch ICs and such. I have no problems with 0603, could go to 0402 no problems but it just doesn't offer enough benefits to warrant the change for me.Edit: I don't even own a magnifying glass or a loupe or anything. I do have a USB microscope but I don't use it with passives. Just to check some QFN:n solder joints and such.

author: pyrohaz
author_rank: Regular Contributor
timestamp: July 09, 2014, 08:20:50 am
content: I've made PCB's with 0603, 0805 and 1206 parts. Obviously 1206 is easiest and have the advantage of running low speed tracks underneath the components (two tracks can generally fit with 0.2mm spacing) making PCB routing a touch easier. 0805 components can generally allow one track to run underneath the component and are still pretty easy to solder. I've used 0603 for my watch project (http://hsel.co.uk/2014/06/17/eon-smart-watch-3/) with little extra effort though too much solder causes the components to sometimes suck into the iron which is annoying! They also weigh near to nothing and can blow around relatively easily.I agree with the majority of other people here, starting with 0805 is good and if you manage that, 0603 shouldn't be a major problem! My current configuration is resistors at 0603, jumpers (0r resistors) 1206 (to allow for two tracks below on single sided boards) and capacitors at 1206 to support all capacities.Enjoy SMD!

author: suicidaleggroll
author_rank: Super Contributor
timestamp: July 09, 2014, 04:43:21 pm
content: Quote from: SirNick on July 08, 2014, 10:18:02 pmJust watch out for the effects of DC bias in those small ceramic caps. The smaller you go, the worse it gets. 1206 and 0805 aren't too bad, but when you get down to 0603 or 0402, the decoupling capacitance you get from an MLCC is only maybe 20-40% of its rating, depending on the manufacturer/model and the voltage you're trying to decouple.

author: cellularmitosis
author_rank: Unknown
timestamp: July 09, 2014, 05:21:40 pm
content: Having gone through the ContextualElectronics course, I transitioned from being a militant "through hole only" guy to a "SMT is ok but stick with 1206 if you can" guy.I find 0805 just on the verge of being annoying to solder by hand. Sounds like I'm in the minorityHowever, using a reflow oven would probably make 0805 less of a hassle than hand soldering.

author: SirNick
author_rank: Frequent Contributor
timestamp: July 09, 2014, 07:11:24 pm
content: Quote from: poorchava on July 09, 2014, 05:49:30 amDuh, of course! Thanks!Quote from: suicidaleggroll on July 09, 2014, 04:43:21 pmThanks for the heads-up. I read up on ceramic ratings on Wikipedia (and watched Dave's video on this topic), but I wasn't aware it had any correlation to size. Good to know.Quote from: cellularmitosis on July 09, 2014, 05:21:40 pmIt certainly can be. The resistors in particular appear to have a nasty habit of sticking to the iron's tip instead of the pad. And, of course, if you drop one into the carpet, you have a 50/50 chance of ever seeing it again.

author: Neilm
author_rank: Super Contributor
timestamp: July 09, 2014, 07:49:34 pm
content: Smaller caps have different frequency profiles due to the parasitics in the construction. If you are working at higher frequencies (or very fast switching edges) the cap size becomes important due to the reduction of the parasitics and the higher frequencies they can handle rather than how easy they are to solder.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: July 09, 2014, 08:39:11 pm
content: Quote from: SirNick on July 09, 2014, 07:11:24 pmHere's a short article with some examples, showing how significantly it can change with package size:http://www.edn.com/design/analog/4402049/2/Temperature-and-voltage-variation-of-ceramic-capacitors--or-why-your-4-7--F-capacitor-becomes-a-0-33--F-capacitor

author: zapta
author_rank: Super Contributor
timestamp: July 10, 2014, 10:19:03 pm
content: Quote from: suicidaleggroll on July 09, 2014, 08:39:11 pmDo LCR/ESR meters allow to measure with different capacitor bias voltages?

author: TheRuler8510
author_rank: Regular Contributor
timestamp: July 10, 2014, 11:42:22 pm
content: Quote from: zapta on July 10, 2014, 10:19:03 pmIn general, no...but there are specialized ones that do allow bias voltages, like the HP4261A.

author: calexanian
author_rank: Super Contributor
timestamp: July 11, 2014, 05:17:59 am
content: I do all of our SMD short run and proto boards at our shop. 0805 is the most practical for hand place. Any smaller adds time for alignment. I have lately been having stencils unlimited make stainless stencils and them flowing the boards with a hot air station. TQFP chips I still prefer to drag solder. My eyes going buggy is my limiting factor. Magnification or not, its tough and I can only place parts for about an hour at a time.