Using 0402 when plenty of room for 0603 - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: May 03, 2023, 07:12:12 pm
content: Hi,We are doing a LNK3209 based Buck converter. The designer has used all 0402 resistors for the auxiliary resistors around the control chip. There is bags of room for 0603's but he used 0402 instead.Do you agree this is a very bad idea?0402 doesnt allow the value to be checked by checkers in the PCB assembly house.Also, 0402 needs the board temperature to be within a much tighter tolerance than 0603 resistors during surface mound soldering."Head on pillow" is far more common with 0402 than 0603...partly as the 0402 is lighter and can "tomb up" much more readily.

author: floobydust
author_rank: Super Contributor
timestamp: May 03, 2023, 08:00:28 pm
content: Quote from: Faringdon on May 03, 2023, 07:12:12 pmHow is it that "we" are doing the "converter" but an idiot is spec'ing 0402's? That sounds like your preferred way, too small for your own good in a SMPS with large through-hole parts. 0402 saves nothing at all.

author: SMTech
author_rank: Frequent Contributor
timestamp: May 03, 2023, 08:33:09 pm
content: Quote from: Faringdon on May 03, 2023, 07:12:12 pmNo, I don't. 0402 is increasingly standard for many designers, also don't want to break your bubble but you may have noticed the values disappearing from 0603 and 0805 resistors too. However if you are doing very low volumes and not using a proper assembly line, sure you'd be better off with larger parts just because they are easier to fiddle with or handle with tweezers. Your assembly concerns are unfounded unless your process sucks.

author: asmi
author_rank: Super Contributor
timestamp: May 03, 2023, 08:43:06 pm
content: Quote from: Faringdon on May 03, 2023, 07:12:12 pmAbsolutely disagree, and I use 0402 everywhere I can because 1) they are the cheapest 2) they take the least amount of space on a PCB.Quote from: Faringdon on May 03, 2023, 07:12:12 pmPCB assembly house can't afford a multimeter?Quote from: Faringdon on May 03, 2023, 07:12:12 pmQuote from: Faringdon on May 03, 2023, 07:12:12 pm

author: Feynman
author_rank: Regular Contributor
timestamp: May 04, 2023, 05:56:41 am
content: Maybe it's your company's default size, because of price, availability and space constraints on other boards. A consequence might be that your company's in-house stock for prototyping and repair is mainly 0402. Or the EMS is storing a large quantity of 0402, because most boards your company is ordering are 0402. Maybe your company or the designer has some well established fan-out patterns for 0402. For example, how vias are placed at a decoupling capacitor, how a resistor network is placed around an operational amplifier, etc, etc, ...There could be many more reasons for using 0402 although there is enough room for 0603 and even bigger ones.But having a standard size you don't deviate from without strong compelling reasons is definitely advantageous. And 0402 is becoming increasingly more popular as a standard size.You have to be a little more careful with the parameters of 0402 parts compared to 0603, especially with capacitors. However, you cannot be careless with parameters of 0603 either...For most EMS 0402 is as "jelly-bean" as 0603 and there shouldn't be any soldering issues if you stick to the EMS's recommended land pattern.

author: Faringdon
author_rank: Super Contributor
timestamp: May 04, 2023, 08:46:01 am
content: QuoteThanks...on that basis, then why not use 0201 instead of 0402?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 04, 2023, 08:57:50 am
content: Quote from: Faringdon on May 04, 2023, 08:46:01 amBecause of the tradeoff between size and useability - 0201 needs much more care for assembly, more expensive feeders , more precise placement and paste print, and is much harder to rework.The sweet spot depends a lot on other factors - what sort of machine it's assembled on, volumes etc. For hand assembly, 0805 is the optimal compromise between size and assemblability, for low-end pick/place, 0603, for higher-end pick.place 0402.The only reason to use 0201 or smaller is where you absolutely need the smaller size

author: loki42
author_rank: Frequent Contributor
timestamp: May 04, 2023, 09:55:30 am
content: The default size thing I think is very sensible. I don't stock any 0603. 0402 fit more on a reel, take up less space on the board and are easy to place / paste. Having a reel of the same value in a different size would be annoying. I do use 0805 for larger caps like 22u.

author: Reckless
author_rank: Frequent Contributor
timestamp: May 04, 2023, 09:59:19 am
content: Quote from: mikeselectricstuff on May 04, 2023, 08:57:50 amAre they still more expensive than 0402? I would like to move to 0201 but they have been more expensive than 0402.

author: tooki
author_rank: Super Contributor
timestamp: May 04, 2023, 01:08:09 pm
content: Quote from: Faringdon on May 04, 2023, 08:46:01 am0402 are the cheapest. Ergo, 0201 must costmore. (And they do.)As you go smaller from 0402, cost increases, so you only use smaller components when board space or parasitic inductance need to be minimized.Why does price increase as you go smaller or bigger than 0402?You’ve got two size/cost curves: one for materials cost, and one for handling cost (both in component manufacturing and in board assembly).Obviously, materials cost goes up with size, since you need more of it for larger components. So making them smaller reduces the materials cost. But at some point, the components get so small that they’re harder for the machinery to handle, so that curve goes up as the size shrinks. The cheapest components are where those two curves intersect, and today, that’s 0402. Anything smaller requires more advanced pick and place machines, which not all assembly houses may have, and those that do might not have those machines on every production line. And IIRC, they may not be as fast with the tiny components. Sticking with 0402 and larger means the older and/or faster PnP machines can be used, lowering assembly cost.

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 04, 2023, 01:26:46 pm
content: If there is something that the past year’s component shortage taught everyone, is that the design must follow a package’s “sweet spot” in terms of price AND availability.Right now, the 0402 package seems to have consolidated that sweet spot.A company I consulted for, had a strict policy of 0603 components, back when these were the sweet spot.You may ask: what happens when the applied voltage causes the component to exceed its voltage or power rating? Then you use two or more devices in series.There were exceptions to the rule, of course. Supply filter caps were 1210 in size. Likewise some mili ohm shunt resistors.

author: asmi
author_rank: Super Contributor
timestamp: May 04, 2023, 01:30:33 pm
content: Quote from: Faringdon on May 04, 2023, 08:46:01 am1) 0201 parts are more expensive than 0402.2) the tech to handle anything <0402 is too expensive at this time.3) I can handle 0402 manually (under a stereo microscope), working with 0201 is much harder.

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2023, 01:38:53 pm
content: If you've got loads of space, then how about designing the board so it will take either 0603 or 0402? That way you can use whatever you can get hold of.Incidentally, I'm working on an H-bridge with opto-coupler MOSFET drivers and will design the PCB, so it will fit different types of opto-couplers and possibly MOSFETs, so I don't face supply problems. The marginal increased cost of the PCB will be worth it.

author: Faringdon
author_rank: Super Contributor
timestamp: May 04, 2023, 06:07:37 pm
content: Thanks, do you mean a single footprint that will take either 0603 or 0402...ive been told off for doing that in the past...told the 0402 could slip about during solder bath , and not be soldered properly?

author: coromonadalix
author_rank: Super Contributor
timestamp: May 04, 2023, 06:34:59 pm
content: avoid 0402 if possible .......... thoses pesky ...but for part number or values written on themfor sure they love to makes a mess before on bigger parts you had say written "101" for the value who was easy to decode etc ...and now on some parts it "a21" or something like this

author: asmi
author_rank: Super Contributor
timestamp: May 04, 2023, 06:45:34 pm
content: Quote from: Faringdon on May 04, 2023, 06:07:37 pmDon't do that, you will have problems during assembly with such footprints - unless you intend to assemble those boards manually.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 04, 2023, 07:11:27 pm
content: You have to be making a colossal quantity of things if the relative cost of resistors matters.

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2023, 08:11:07 pm
content: Quote from: Faringdon on May 04, 2023, 06:07:37 pmNo. I was talking about separate footprints, not one for both.

author: nimish
author_rank: Regular Contributor
timestamp: May 05, 2023, 05:03:30 am
content: A fun corner case is that decoupling capacitors are principally limited by package inductance, so shrinking them is required for them to do much at higher frequencies. The capacitance itself doesn't matter that much. So going from 0402 back up to 0603 might cause more problems than you solve.

author: Faringdon
author_rank: Super Contributor
timestamp: May 05, 2023, 08:07:02 am
content: I think if you have your own in-house SMD machines, and do you own board stuffing, then 0402 is ok...but if you are using external board houses, and your volumes are nt massive, then they never do the temp profile right, and you end up with 0402 with "head on pillow"...this happens less with 0603........its just the truth.......board stuffers dont know how to perfectly set their machines, and in truth, every different board needs a different temp profile, and unless they are dedicated to that board, they wont get the temp profile exactly right, and you get head on pillow with 0402

author: SMTech
author_rank: Frequent Contributor
timestamp: May 05, 2023, 08:16:22 am
content: Quote from: Faringdon on May 05, 2023, 08:07:02 amHorseshit. I can run a pretty much the same profile for just about any board of similar mass, the measured profile will be broadly the same. The thermal headroom on modern reflow is massive, if you see issues outsourcing, your layout is bad.

author: HighVoltage
author_rank: Super Contributor
timestamp: May 05, 2023, 08:16:55 am
content: Quote from: Faringdon on May 05, 2023, 08:07:02 amThis was a problem 10 or 15 years ago but not today.I use 0402 all the time, especially for buck converters and there is really no problem in manufacturing.And 0402 can still be soldered by hand for prototyping.

author: nali
author_rank: Frequent Contributor
timestamp: May 05, 2023, 08:54:49 am
content: Quote from: Faringdon on May 03, 2023, 07:12:12 pmI can't be the only one wondering what "doing" means in this context..?I've worked with 0402 in smart meter products on boards with extensive copper pours and connections to fairly massive busbars, no problem although can be a pain to rework. IIRC the only 0603 & 0805 were ceramic caps.

author: Faringdon
author_rank: Super Contributor
timestamp: May 06, 2023, 11:09:35 am
content: Analysis of failure returns.......surely easier with 0603 as you can see what value they are.Ditto Board stuffers QA dept doing 10%_of_batch checks....they can check the 0603 value, not so 0402.When in cct, often they cant be reliably measured.I worked in one place, where the guy soldering up the 0402's in the prototypes, used to use a weller iron, with the wrong tip in it.....so as to reduce thermal contact.....which stopped the pesky 0402's from getting sucked into his soldering iron when he soldered them..(when he removed the soldering iron, the solder would "follow" the iron, and dislodge the 0402 he had just soldered.)All would agree, they are much worse for product prototype testing point of view.Never yet seen a "head on pillow" 0603......seen many H.O.P 0402...seen more tombstoned 0402 than 0603.Admittedly people get bullied in to 0402 by the board stuffer, who wants to keep stock room low.

author: tooki
author_rank: Super Contributor
timestamp: May 06, 2023, 11:14:42 am
content: You know they’re now getting rid of markings on 0603’s, right? (Which I hate, but so it is…)As for the rest of those arguments: I’m sure that people who were used to THT resistors used to say the same things about 1206, then 0805, and then 0603, too.And as for the soldering technician: I guess nobody told him about these magic things called “tweezers”.

author: Faringdon
author_rank: Super Contributor
timestamp: May 06, 2023, 11:51:21 am
content: thanks, ayk, its much easier to tweezer_grab an 0603 than an 0402

author: ebastler
author_rank: Super Contributor
timestamp: May 06, 2023, 12:08:50 pm
content: Quote from: Faringdon on May 06, 2023, 11:09:35 amUmm... I thought the "head on pillow" defect is specific to BGA packages. If the BGA's solder ball and the solder paste on the board do not fully melt and coalesce, the BGA ball forms a "head" which rests on the "pillow" of solder paste. What do you mean by a "head on pillow" problem with 0402 resistor packages?

author: Faringdon
author_rank: Super Contributor
timestamp: May 07, 2023, 11:58:53 am
content: thanks, H.O.P. is like the 0402 res is lying on the pads...and looks properly fitted from a distance, but if you get the magnifying glass...you see one of the pads is lying on top of the solder, and is not melted into it.Seen this on loads of production failed boards.

author: Niklas
author_rank: Frequent Contributor
timestamp: May 07, 2023, 01:31:17 pm
content: I work with an automotive design with 0402 sized resistors and capacitors mounted on both sides of the PCBA. The footprints are minimum according to IPC 7351, dense layout, no rework and IPC-A-610 class 3 acceptance. Even with some of the components connected directly to copper polygons, there are no issues with tombstoning. The key is to have control of symmetry between the pads and check the solder pad recommendations from the different alternatives. Some of this can be handled by adjusting the solder mask to define the effective pad size on the polygon end to match the copper defined pad.

author: tooki
author_rank: Super Contributor
timestamp: May 07, 2023, 02:55:14 pm
content: Quote from: Faringdon on May 07, 2023, 11:58:53 amSo simple non-wetting.There are many things that could cause that, none of which are specific to 0402 parts.

author: Faringdon
author_rank: Super Contributor
timestamp: May 07, 2023, 06:30:55 pm
content: QuoteSo you are saying that 0402s are ok, as long as you go through the layout, and adjust the polygon side pad so its solder mask defined.......that tells me that 0402's are "with difficulties".

author: Infraviolet
author_rank: Super Contributor
timestamp: May 07, 2023, 07:44:53 pm
content: One other point to add, which hasn't been mentioned yet.In terms of PCB routing 0603 can actually be easier to work with, with common design rules for trace spacing and minimum width (0.2mm for each) it is very easy to route under an 0603 between its pads (0.9mm gap), not feasible to route under an 0402 (0.5mm gap < 0.2clearance+0.2width+0.2clearance). 0603 has the advantage here then, when you've got boards with two (or one) copper layers, and a board house with 0.2mm design rules.My own circumstances are that I use 0603 mostly, for ease of hand-assembly, with 0805 for anything polarised like SMD LEDs. But unlike most of the arguments in favour of 0603, this one about routing underneath still holds for machine assembled boards too.

author: asmi
author_rank: Super Contributor
timestamp: May 08, 2023, 12:13:21 am
content: Quote from: Faringdon on May 07, 2023, 06:30:55 pmThe only one who seems to be having difficulties is you. I have assembled 100's of boards with 10's of thousands of 0402 parts, and I only ever got a SINGLE case of a tombstone (and one 0201 tombstoned on another occasion). Heck I get more soldering problems with QFNs than with 0402 (or even 0201)!

author: asmi
author_rank: Super Contributor
timestamp: May 08, 2023, 12:17:44 am
content: Quote from: Infraviolet on May 07, 2023, 07:44:53 pmThat's yet another argument from the pastTake a look at the calendar, it's year 2023 now, even super-cheap low-end PCB fabs have no problems manufacturing 0.1/0.1 mm traces, JLCPCB can do 0.09/0.09 mm traces, some other affordable fab I use (WellPCB) can go down to 0.08/0.08 mm. And that is just a regular process, not HDI or other sort of special process.

author: 48X24X48X
author_rank: Frequent Contributor
timestamp: May 09, 2023, 08:32:57 am
content: I think 0402 reflow yield is very good and I tend to like their joints more than 0603. As someone that assemble own board, I would love to use 0402 as much possible but having only a 4-head machine, it would make placement too slow as you need more nozzle variations to cover all component sizes. 6-head would be minimum, or better 8-head, or okay it never end... As it stands now, I only use them at the RF tuning circuit.

author: SMTech
author_rank: Frequent Contributor
timestamp: May 09, 2023, 09:19:51 am
content: Quote from: 48X24X48X on May 09, 2023, 08:32:57 amThis is the reason Toolchangers exist... and why I'd never buy a machine without one.

author: Microdoser
author_rank: Frequent Contributor
timestamp: May 09, 2023, 12:34:07 pm
content: After reading this thread, I think I'll get in some 0402 resistors and gain some wriggle space on my latest board...

author: ebastler
author_rank: Super Contributor
timestamp: May 09, 2023, 01:23:34 pm
content: Quote from: Microdoser on May 09, 2023, 12:34:07 pmHand-placing them with tweezers is significantly more fiddly than with 0603s though, in my experience. Buy some extra 0402s to fling across the room, never to be seen again...

author: HighVoltage
author_rank: Super Contributor
timestamp: May 09, 2023, 02:41:52 pm
content: Quote from: ebastler on May 09, 2023, 01:23:34 pmThe way I do this:- Apply some solder paste to the PCB pads- Use tweezers to lay down the 0402 part carefully- use some small angled pliers and lay down one wing on to the 0402 part (2 handles on the table)- use the solder iron and just touch the PCB pad and it will solder right away- repeat on the other side of the 0402 partThis has been working for me every time without flying parts across the room.

author: ebastler
author_rank: Super Contributor
timestamp: May 09, 2023, 03:11:55 pm
content: Quote from: HighVoltage on May 09, 2023, 02:41:52 pmStep 2 is where I do the flinging.The 0402 parts slip out of the tweezers more easily than the larger parts. Depending on the amount of pressure I apply to hold them, that catapults them across the PCB, the bench, or the room... Once the part is placed on the PCB, everything is fine, both for hot-air or conventional soldering.(Yes, I do have decent tweezers, and the majority of 0402 parts makes it to their destination OK. My loss rate is below 10%, I'd say -- but still high enough to annoy me. So I prefer 0603 for boards I intend to populate by hand.)

author: HighVoltage
author_rank: Super Contributor
timestamp: May 09, 2023, 03:36:53 pm
content: Quote from: ebastler on May 09, 2023, 03:11:55 pmI am using tweezers with 90 degree tips, so that the 0402 part is lightly squeezedin parallel.Normal tweezers usually have an angle to the part and then they like to fly away.Actually the best 90 degree tweezers I found for this purpose came from my daughters "make up kit" for precisely removing facial hair!But of course, I agree that 0603 parts are easier to handle by hand.

author: asmi
author_rank: Super Contributor
timestamp: May 09, 2023, 05:09:24 pm
content: Quote from: ebastler on May 09, 2023, 01:23:34 pmNot if you have the right equipment like stereo microscope and a good vacuum pickup tool (cheap crap from Aliexpress is not that). I place 0201 caps using the same equipment, though it is somewhat harder because even under 10x magnification these things are rather small.Quote from: ebastler on May 09, 2023, 01:23:34 pmI buy them by reels on LCSC because they are so cheap, so even if I lose some, who cares - there are 10K parts on a reel.

author: ebastler
author_rank: Super Contributor
timestamp: May 09, 2023, 05:31:19 pm
content: Quote from: asmi on May 09, 2023, 05:09:24 pmI do use a stereo microscope and find it helpful -- seeing things better improves the placement precision, and I feel that the higher-resolution in the hand/eye feedback loop also gives me a steadier hand.Which vacuum tool do you recommend? I played with vacuum pickups a while ago, mainly for hand-placing some BGA packages which were too wide to grab with tweezers. The cheap (Aliexpress style) manual tool was crap indeed. I also experimented with a home-built design with a motorized pump, but could not find a good position for the "release" hole on the handpiece: Lifting a finger to release the part would make me shift its position most of the time. So I'd appreciate a reommendation!

author: asmi
author_rank: Super Contributor
timestamp: May 09, 2023, 06:37:19 pm
content: Quote from: ebastler on May 09, 2023, 05:31:19 pmYeah, when I bought the microscope, I realized that my hands are capable of much more precise movements when I can actually see them. I use AmScope SE410 with 10x magnification for regular work, and 20x when working with 0201s or when I do solder joins inspection. I've taught my wife to solder and assemble PCBs, and she loves the microscope, so much so that she even does her nails under it nowI'm planning to upgrade it to trinocular version on a dual-arm boom eventually - with a camera so that I can show my wife something under it (currently it's very clunky because there are only two eyepieces, so only one person can see at a time), and dual-arm for easier positioning of a head, but if you work alone, binocular head is more than sufficient (unless you want to make photos/videos under microscope of course).Quote from: ebastler on May 09, 2023, 05:31:19 pmThis is the tool I use:https://zeph.com/zt3web.htmIt's got multiple tips available to work with everything from 01005 to big BGAs. It's not cheap, but if you are serious about assembly, this investment is absolutely worth it! Placing small stuff with it is a breeze!

author: NorthGuy
author_rank: Super Contributor
timestamp: May 09, 2023, 07:03:44 pm
content: Quote from: ebastler on May 09, 2023, 05:31:19 pmI use a tee on the air hose which I can open and close with the thumb of my other hand without disturbing the hand piece.

author: langwadt
author_rank: Super Contributor
timestamp: May 09, 2023, 07:13:12 pm
content: Quote from: ebastler on May 09, 2023, 05:31:19 pma 3/2 solenoid valve and a footpedal?

author: asmi
author_rank: Super Contributor
timestamp: May 09, 2023, 07:32:21 pm
content: Quote from: NorthGuy on May 09, 2023, 07:03:44 pmThe tool that I use releases small parts automagically once they touch the board. I'm not exactly sure how that happens, my best theory is that the tip is hard enough such that as soon as part touches the board, it changes it's spacial orientation slightly and this way a small hole opens between the tip and a part, which removes vacuum and so part is no longer held on a tip. Those tips is the biggest difference between handmade tools and the one I use, they are made from some special material which prevents parts from sticking to it (common problem when handling small parts with tweezers), it's soft enough such that it won't damage delicate parts, but hard enough to allow such "automagical" release.

author: ebastler
author_rank: Super Contributor
timestamp: May 09, 2023, 08:29:36 pm
content: Great suggestions, thank you all!I actually have a solenoid valve and footswitch in the drawer which I wanted to add to my homebrew vacuum tool. Ended up rigging up a little support fixture for the pipette instead, which was helpful for the BGA placement (where one has to position XYZ and three rotational axes quite precisely -- beyond my coordination skills, it seems... I love the simplicity of the T junction though, and might try that too.And I am intrigued by the "automagical" release idea. The zeph.com/zt3web.htm page showsDelrintips for small parts, I assume those are the ones? They do sell them separately, but at quite a hefty price, $34.50 (plus international shipping & customs for those outside North America). I will look around a bit; found several other US distributors of what looks like the same tips, at similar prices, but none in Europe so far.

author: Microdoser
author_rank: Frequent Contributor
timestamp: May 09, 2023, 09:47:21 pm
content: I think I'll see how my normal method works on a test board. Use a pair of tweezers that have a little residue on them from the previous component's solder paste. Not a lot, just enough to pick up a tiny resistor/cap and which sticks slightly less than the solder paste on the board does.I've already accepted some component loss as a part of working with things so small. I may as well get the extra board space, and reduce part costs at the same time.I assume they are as reliable as 0603?

author: c64
author_rank: Frequent Contributor
timestamp: May 10, 2023, 03:08:04 am
content: Quote from: NorthGuy on May 09, 2023, 07:03:44 pmI use exactly the same. Cheap $10 vacuum pump from China (running at half voltage - more than enough suction), hose with hole and tips from crap Chinese vacuum pickup tool. Never use tweezers any more