Which SMD package to go for ? - Page 1
Forum section: electronics / beginners

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 01, 2017, 04:08:49 pm
content: Hi all,I have a few smd components that I need to my project and that is something new to me.Could anybody please advise me on the SMD package to go for. This is basically an FTDI interface that I am adding to my pcb so just two resistors, a cap, two LED and the FT232RL is all I would need for SMD part of the design.Sent from my iPhone using Tapatalk

author: oldway
author_rank: Super Contributor
timestamp: August 01, 2017, 04:21:36 pm
content: SMD resistors has power and voltage limitations...I like using 1206 resistors... (0.1W max)

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 01, 2017, 04:32:00 pm
content: Thanks the FTDI schematic from sparkfun uses 402 and they seem to fit in my pcb. What would be difference other than the size. Does size matter is it just up to designer ?Sent from my iPhone using Tapatalk

author: NivagSwerdna
author_rank: Super Contributor
timestamp: August 01, 2017, 04:50:58 pm
content: If your design has plenty of space then you have a free hand to decide the size of components.Firstly I used 0805 for everything, these are relatively large and easy to solder. Now I tend to use 0603 (you can normally solder these onto 0805 footprints if you want to hedge your bets) as they are very very cheap.The size may be determined by how you intend to assemble the components.Smaller components tend to have lower current ratings and in some cases the minimum package size will be determined by the value you need.

author: MattHollands
author_rank: Frequent Contributor
timestamp: August 01, 2017, 05:46:06 pm
content: I generally go for 0603 but I generally loose 1 in 10 components so make sure you have spare. If you have the space though, you might as well go 0805. Depends how good your eyes are, how steady your hand is, how much patience you have and how much space you have on the board.Make sure to use lots of flux when soldering SMD parts.

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 01, 2017, 06:07:06 pm
content: Thank you guys that was quite some info. I will just check the size on you tube just to get an idea how small these things are before I order them. These 402, 603 and 805 are these the size of the package ?Sent from my iPhone using Tapatalk

author: suicidaleggroll
author_rank: Super Contributor
timestamp: August 01, 2017, 06:26:23 pm
content: Quote from: anishkgt on August 01, 2017, 06:07:06 pmThe sizes are the dimensions of the package in hundredths of an inch. So an 0402 is 0.04" x 0.02", an 0805 is 0.08" x 0.05", etc.With a microscope, I'm comfortable down to 0402 and I can go smaller, but don't quite enjoy it. Without a microscope, 0603 is about at my limit...0805 is quite a bit easier.I typically do 0603 as a default, 0402 if I need to due to space reasons, and 0805 if I have an overabundance of space that I don't know what to do with.

author: bson
author_rank: Unknown
timestamp: August 01, 2017, 08:11:57 pm
content: Start with 0805 for your first project; they're very easy to work with.They will come on a section of tape off a reel intended to be used in a pick & place machine; either peel the clear side as needed, or dump them into a suitable container. I generally buy 0402 resistors by qty 250 and dump them onto a sheet of paper with a fold in it, then keep them in one of these:https://www.amazon.com/dp/B00A15YHJY. This is a HUGE benefit of using SMD - I have 8 of these (in various variations, but the one shown is the one I find works best); that's almost 1000 different parts, and probably around 100k components. The stack takes almost no space on a storage shelf! And, as you've noted, it takes several hundred quality SMD film resistors (I like Susumu RR and RG for general purpose) to add up to even a couple of dollars from a reputable distributor. Same with caps (I like Kemet, forget the series off hand).

author: rstofer
author_rank: Super Contributor
timestamp: August 01, 2017, 08:24:58 pm
content: And don't cough or sneeze!I usually use 0805 because they are easier to pick up and turn over. By definition, all resistors will be upside down when I pick them up.I don't often hand solder SMDs. I either use a hot plate or a converted toaster oven.

author: KL27x
author_rank: Super Contributor
timestamp: August 01, 2017, 08:40:53 pm
content: To get an idea of the size, picture your board is 10/10 traces. You can place a 0201 resistor right over a trace and it will disappear.An 0402 can be put on same trace without bridging the surrounding traces. So think about it. If you use these small of resistor, you don't even necessarily need to add any space to place pads!When you order, make sure you check your units. SMD parts also come in metric. The metric 1206 is a different size. Imperial is more the standard.Size of parts matters because of how hard it is to handle. An 0402 requires a very fine needle for the pickup, which makes it easier to clog and useless for larger parts. 0603 can use 25 gauge needle which will pick up bigger SOT23 and SMD caps and such without swapping needles as often. Regarding tweezers same problem. Smaller parts tend to be harder to get a hold of in the proper place and will much more easily stick to the tweezers wrong.Tip: while soldering, if you get SMD part stuck to the tweezers due to flux, stick the tip of your iron to the tweezer until it falls off.As far as IC's are concerned, for DIL I prefer SSOP as the smaller that is easily soldered to a pcb when considering IC's 14 pin and larger, and SOIC for the small 8 pin stuff (just because the SSOP get oversquare and probably best used in tape,,, which is pain). But for prototyping with veroboard/breadboard, they are evil. But when choosing between quad packs, I actually prefer QFN over QFP for packaging reasons. Trays of QFP are a PITA.For passives, where size and dissipation doesn't matter, I tend to go 0805 for the resistors. For decoupling caps, 0603 tends to be cheaper for given voltage rating. Caps are also easier to handle because they are heavier.Sidenote: Some 0603 resistors are marked with value. I've never seen 0402 that is marked, although I bet there are some. All 0805 and larger I have ever used have the value marked on top. This is a slight bonus when prototyping.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: August 01, 2017, 08:44:53 pm
content: https://en.wikipedia.org/wiki/Surface-mount_technology

author: medical-nerd
author_rank: Regular Contributor
timestamp: August 01, 2017, 11:26:22 pm
content: HiyaI have just started with surface mount, using a simple magnifier from ebay (photo attached) I can comfortably hand solder 0805, SOT-23, SOIC and SSOP components. I was pleasantly surprised that I could achieve this without complex or expensive equipment.Cheers

author: poorchava
author_rank: Super Contributor
timestamp: August 02, 2017, 06:43:52 am
content: I started with 0805 and had no problems whatsoever having no previous experience with soldering SMD at all. Now i routinely use 0603. I like them more than 0805 for building stuff on universal pcbs, as the contact typically ends just at the edge of the pad making it possible to solder something THT or a wire into the hole in that pad.I use 0402 when I have to. Soldering is not difficult, just requires some prectice to master. Also, having thermal reliefs for anything that connects to even a small copper pour are a must, since you'll generally be using a rather fine tip that has very little heat capacity. Another thins that is much more annoying with 0402 as compared to 0603 is that when you tack one end of a passive to a pad and heat up the other electrode to apply solder, after like 2-3 seconds, the tacked terminal will get hot enough to melt and the component will get displaced. I find it that quite often it is easier and faster to solder 0402 by tinning the pads, applying flux and then soldering the component using hot air station with a thin nozzle.

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 02, 2017, 07:20:00 am
content: I use the hackko soldering with chisel tip and would solder flux in a paste form be ok with SMD ?And no narrow tip but just a hot air gun.Sent from my iPhone using Tapatalk

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 02, 2017, 07:23:31 am
content: Quote from: medical-nerd on August 01, 2017, 11:26:22 pmI have one similar to this but the alligator clips are pain. Looking for swirl type ones and yes the led is an advantage.Sent from my iPhone using Tapatalk

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 02, 2017, 07:40:05 am
content: In a schematic for basic FTDI breakout board from sparkfun the is a cap of 10uf but the voltage is not mentioned would it be above 5v like 6 or maybe 10v ? how do we choose the appropriate SMD cap here. C5 in the schematic looks electrolytic would a similar SMD be thishttps://www.digikey.com/product-detail/en/avx-corporation/F951A106MPAAQ2/478-8417-1-ND/4005591?schematichttps://www.sparkfun.com/datasheets/DevTools/Arduino/FTDI%20Basic-v21-5V.pdfSent from my iPhone using Tapatalk

author: djnz
author_rank: Regular Contributor
timestamp: August 02, 2017, 08:43:08 am
content: 1. As the max voltage they will see is around 5V, I'd use capacitors rated for 10V or more in this application (some safety margin). For this application, X7R dielectric should be fine, no need to spend more money and board space on NP0 / C0G.2. Part sizes are commonly specified in 1000th of an inch, but sometimes, also in metric units (0.01 mm), so watch out for the system used. For example, 0805 is 2012 metric.3. I avoid using tiny parts if I can get away with using bigger ones. If you can get away with using 1206 or 0805, why have the hassle of soldering ultra tiny 0201 parts?4. You will need good tweezers to solder tiny parts by hand. Solder wire thickness also matters and you will want to use thin solder for soldering tiny parts. I also like to use extra flux (over what comes embedded in the solder wire.5. For soldering really tiny parts, you will want a soldering iron that gives you more control - so the distance from the handle where you hold the iron, to its tip, should be small and the iron should be light in weight.

author: Gyro
author_rank: Super Contributor
timestamp: August 02, 2017, 09:10:48 am
content: Quote from: anishkgt on August 01, 2017, 04:08:49 pmIt really depends what you're planning to do, going forward. If two resistors and a cap are your only requirement, then you may as well use 1206... or even 1/8 through hole, as your USB socket and headers(?) presumably will be too.If you're goning to make a habit of smd passives then I'd use a size range, centered on 0805. You can also keep a limited range of 0603 and 1206, there's no reason to completely stick to one size.Reasons as follows:1. Center on 0805 because it is easy to get track(s) between the pads without going too fine on geometry. Resistor values are marked. Easy to handle with tweezers. Reasonable cost (not as cheap as 0603 but not as expensive as 1206).2. Use 1206 for occasions where needed for power dissipation or voltage rating (also achievable by parallel / serial 0805 combinations). Also (maybe) on the odd occasion where routing requires more tracks between the pads - if it saves jumpers or more layers then the extra cost would be worth it. Reserve them for 'special' occasions.3. Use 0603 where space is tight. Price saving over 0805 probably isn't a good enough reason on its own. Still handable with tweezers but harder to get a good solder profile on capacitors (package cracking on board flex). The smallest size where you can sensibly route tracks between pads but you're limited compared to 0805. As NivagSwerdna says, you can fit 0603 onto 0805 pads, but you loose the space saving advantage and they are much more likely to tombestone if you later decide to take a board to reflow.4. Avoid 0402 unless you're building a mobile phone or similar (yes I know they mostly use 0201 these days). The lack of resistor marking and increased pain in handling just makes them too much hassle for hand assembly compared to the others - might be different if you're doinghighfrequency RF. I'm not sure if there is still a low volume cost penalty against 0603 these days.Those are the about only factors I can think of, off hand.