SMD prototyping techniques -- looking for advice - Page 1
Forum section: electronics / projects

author: ebastler
author_rank: Super Contributor
timestamp: July 27, 2019, 10:53:52 am
content: So far, I have still been building my prototypes mainly with through-hole components. (Mostly digital/µC, some audio-range analog, some analog up to a few MHz). I mainly use 2.54mm pitch protoboard with square pads, and solder on Kynar-wire connections. Where SMD ICs were required, I have either used little adapters to DIP footprint, or soldered SOICs directly onto the protoboard with every other pin bent up and wired free-floating.That kind of works, but with more and more ICs becoming avaiable in SMD-only style, it has become more and more awkward. It feels like it's time to move to SMD as the "default" prototyping technique. I could use some advice here:(a) What protoboards do people use? Is there an equivalent of the generic 2.54mm square grid -- something like pads without holes but in 1.27mm pitch? Does that even make sense, assuming I can largely stick with SOICs? What do you do if you need higher-density packages?I am aware of the various SMD protoboards which carry an assortment of specific TSSOP etc. footprints. But these seem rather limiting, almost to the point where you need to know your designs's chip complement before you order the protoboard. If these are the way to go, how do you work with them? Or is it back to individual DIP adapters? if you need to mix and match various SMD packages in a circuit?(b) What is your personal "sweet spot" size for passive? 0603, 0805? I would want to order E12 or E24 sets of resistors and capacitors, but only in a single mechanical size.(c) I think I have the soldering under control, either pad by pad or using extra flux and dragging the tip. Haven't experimented with solder paste and oven/pan soldering yet, but that would be used for small series rather than early prototyping, right?(d) Any other advice for SMD prototyping? Many thanks in advance for your help!

author: tautech
author_rank: Super Contributor
timestamp: July 27, 2019, 11:10:22 am
content: Watch Dave’s last mailbag for SMD proto boards. I started with 0805 but proved concept on a breadboard therefore needing to use IC’s that are available in DIP and SMD.Once you dive properly into SMD you’ll love it.Oh, and get some SMD smart tweezers before too long.Oh and something else, get some K style Hakko tips or similar, they're great for rework in that they reach both ends of passives so you can grab them with tweezers or sweep them off the pads.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: July 27, 2019, 11:26:07 am
content: I have experimented with SMD breakouts etc but it quickly becomes a major PIA so now I just go straight to PCB... sometimes creating a generic layout that can be part populated and also accept that v1.00 will be unlikely to be the final revision.With DipTrace (or equivalent) and a super cheap 5 or 10-off PCB prototyping service Elecrow (or equivalent) (and a microscrope) it's a joy.Have fun!

author: KE5FX
author_rank: Super Contributor
timestamp: July 27, 2019, 11:32:13 am
content: Meh, everybody makes this 10x more complicated than it really is. You don't need protoboards, just a bare piece of copper-clad board. Flip the chips over, glue them down if you like, and treat their pins, lands, or balls like solder terminals.You will need a good microscope and some very fine wire. It's good to have 30 AWG tinned copper and 40 AWG enameled copper handy. I like to use 0402 parts, but 0603 is OK for most purposes too. (Use the fine wire to provide some stress relief for the MLCCs, or they will break.)Some people like to use gold-plated boards and Dremel tools and multilevel copper islands and other methods to makethistechnique 10x as complicated as it needs to be, but the electrons don't give a hoot how it looks.

author: ebastler
author_rank: Super Contributor
timestamp: July 27, 2019, 11:42:50 am
content: Thank you all for the resonses so far! Thanks for the mailbag hint, I had missed that one.In the meantime, I also found a post by forum member electronic_eel from early last year. His perfboard for combined through-hole and SMD prototypes looks quite plausible to me. (Pads with holes on a 2.54mm pitch, with smaller SMD-only pads fitted inbetween.) Anybody using it? How do you like it, with a year's worth of hindsight?https://www.eevblog.com/forum/manufacture/improved-protoboardperfboard-for-direct-soic-mounting/Quote from: KE5FX on July 27, 2019, 11:32:13 amHmm, I have used that approach for single SMD chips on 2.54mm perfboard, but had not considered it as a general solution for SMD prototyping. How do you mount the passives? Always solder one end directly to a chip pin, have the other end floating?

author: techman-001
author_rank: Frequent Contributor
timestamp: July 27, 2019, 12:46:53 pm
content: Quote from: ebastler on July 27, 2019, 11:42:50 amFor passives you can cut up small squares of single sided pcb and stick them on the blank copper devboard with their copper side up, making 'islands'. The passive then solders to two such squares.

author: Buriedcode
author_rank: Super Contributor
timestamp: July 27, 2019, 01:43:00 pm
content: We live in a great age for electronics prototyping. You can get a pack of SMD-DIP adapters on fleabay, or amazon, aliexpress etc.. for next to nothing. Anything from the standard SOIC, to TSSOP, to QFN.It is also the cheapest its ever been to get quality PCB's made, and delivered to your door in 3 days for $15.That said, I still keep coming back to tri-pad and stripboard for prototyping. SMD-DIP adapters for the IC's, and 0603 or 0805 on the copper side strips. Designed using eagle with the solder/bottom side for the strips, and component/topside for the links. Soldering 0805/0603 is quicker than TH, although without the leads, you have no clippings to use as jumpers. Also of course, the passives can only go between two adjacent strips.A few years ago there was a company, Dip-micro I think, that made thin (1mm) protoboards, with the same layout as solderless breadboards, but with 0.05" pads in the centre for SOIC. These however, we somewhat limited. I've used them a few times, but always go back to cheap stripboard.Another option is a half measure. Making modules for specific devices, that are more than adapters - having extra circuitry, passives, jumpers, sockets etc.. that can plug into 0.1" sockets, or solderless breadboards for prototyping. And using the stripboard as a backplane to interconnection.Working with one-pad-per-hole and kynar is fine, but it takes ages. Especially when there's solderable enameled wire and a propelling pencil ala ELM-chan:http://elm-chan.org/docs/wire/wiring_e.htmlUsing that, with a scalpel and a pair of tweezers, it can be surprisingly quick to connect everything.

author: ogden
author_rank: Super Contributor
timestamp: July 27, 2019, 02:15:44 pm
content: When signal speed is not critical and trough-hole components can do the job - I use perfboard with smd->dip adapters for IC's, through-hole passives with some occasional SMDs if needed. When high frequency is limiting factor, you have to plan layout of your prototype anyway which means - better just route & etch your prototype PCB. Usually I make PCB for just hi-freq RF parts of the circuit, the rest is either MCU devboard or perfboard. I use two-sided presensitized PCB, do not even peel protective film from bottom and obviously do not UV-expose/etch because it will be solid ground plane anyway. Etch just top (circuit & power rail) side, then drill &solder ground vias where necessary, then apply components &connectors.

author: ebastler
author_rank: Super Contributor
timestamp: July 27, 2019, 02:34:54 pm
content: Quote from: Buriedcode on July 27, 2019, 01:43:00 pmHey, thank you for that link. I had come across the web page before (and the video it links to for further illustration), but didn't recall where to look for it. The Kapton tape below the SMD chip packages seems like a nice alternative to the bottom-up mounting suggested by KE5FX -- I would feel more comfortable having the parts oriented like they show up in the datasheet, and being able to read print on the chip package.Yes, wiring things up with Kynar wire can get tedious; and with fine-pitch SMD the room taken up by the insulation can be an issue too. But I have had very mixed success with solderable enamel wire: More often than not, the enamel melting point was higher than desirable, and when it finally melted (burnt?), it left nasty residue behind. Is there a particular brand, or material designation for the "enamel", to look for?

author: tggzzz
author_rank: Super Contributor
timestamp: July 27, 2019, 02:41:00 pm
content: Don't be worried, it is easier than it looks. To my surprise I prefer it to through holeHave a look at my experienceshttps://entertaininghacks.wordpress.com/category/homebrew-pcbs/and techniques inhttps://bristol.hackspace.org.uk/wiki/lib/exe/fetch.php?media=skillshare:solderlessbreadboards03-03.pdfThe only thing I'll add is that removing/replacing SMD components can be done by a solder station "hot air gun" and using polyimide tape to deflect the heat from surrounding components. I've replaced resistors and capacitors on Tek 2465 A5 boards that way. Using an iron can be a problem if you thermally shock a ceramic component by touching it with the bit.Quote from: ebastler on July 27, 2019, 10:53:52 amI mix-and-match a range of techniques, depending on the components and layout.If you can't use a "proper" PCB, there's a lot to be said for dead bug, manhattan, and a dremel with a ball like dentists use.Quote0603 and 0.05mm pitch is easy, provided you have steady hands, tweezers, and good magnification.QuoteEven for one-offs, I successfully use PCB plus solder paste, and a saucepan with a few mm of sand in the bottom.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 27, 2019, 03:14:39 pm
content: Quote from: ebastler on July 27, 2019, 10:53:52 amI always have a few 1.27mm, double sided proto boards available. Usually all square pads, with a few through-holes on one or all sides of the board so you can also solder connectors on or through-hole components, wires or whatever. You can find those easily. Not always for cheap though, but you can find cheaper ones on eBay/ Aliexpress that are good enough.From experience, depending on the complexity of your circuit, it can actually take up more of your time hand wiring all that compared to designing a PCB and have it made for cheap, so most of the time, in my case the prototyping on such boards is limited to small circuits / evaluating some specific IC / etc.Quote from: ebastler on July 27, 2019, 10:53:52 amDepends. Either I can use dedicated (small PCBs) adapters with the required footprint, or I sometimes hand-solder tiny wires on the IC pads (very rare, but I have on occasion).I tend to favor using ready-made breakout boards or evaluation boards though, if available for a reasonable price. A time saver. So I usually look that up first.Quote from: ebastler on July 27, 2019, 10:53:52 amDepends. For proto boards, 0603, 0805 (or larger if required by power dissipation considerations). Anything smaller than 0603 for all-purpose SMD proto boards is a bit nasty.For regular PCBs, there is no sweet spot, it will all depend on size requirements. But I'd say 0603 most often usually. 0402 or smaller if needed. Larger if needed.Quote from: ebastler on July 27, 2019, 10:53:52 amAlso depends, mostly on your habits, available equipment and obviously, components themselves. If a board can be soldered with an iron and/or hot air only, I will do that for the first prototype(s).Now if you have to deal with a lot of components and/or more than a couple BGAs or QFNs, using an oven or pan is worth it.Quote from: ebastler on July 27, 2019, 10:53:52 amA good soldering iron. Lots of flux in various forms: having flux pens, liquid flux and gel flux is all handy. A hot air station. Decent solder wire.And lastly and again, do not shy away from designing proper PCBs and having them manufactured. That's quite cheap and fast these days, and unless you are in a big hurry, you'll have a better time overall.

author: ebastler
author_rank: Super Contributor
timestamp: July 27, 2019, 03:47:39 pm
content: Thanks again for a lot of good advice!Specifically, thanks for the various votes to go straight to a PCB layout for anything with potentially critical HF/crosstalk properties. I have never etched my own PCBs, but have used various cheap Chinese PCB houses quite a bit, and agree that the cost for nicely made PCBs is not an issue anymore. (I have used SMD on some small board designs, and have enjoyed working with them.)My main mental block there is around shipping costs, I guess. Using free standard shipping makes the turnaround time painfully slow. But paying more for expedited shipping than what the actual boards cost feels wrong and wasteful to me -- somehow even more so if it's for an early prototype which I know I will discard eventually... I guess I will just have to get over that!

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 27, 2019, 03:56:10 pm
content: Quote from: ebastler on July 27, 2019, 03:47:39 pmYeah. For us Europeans, shipping from China is either atrociously slow or surprisingly expensive (beware of the various fees and taxes that do not appear upfront!)Nothing much you can do about it... except grouping several PCBs if at all possible. Or use Eurocircuits... shipping not as expensive, but PCBs a lot more.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: July 27, 2019, 06:44:21 pm
content: Quote from: ebastler on July 27, 2019, 03:47:39 pmDifferent manufacturers use different shipping methods... that's once of the reasons I stick with Elecrow because they offer HK Post which is cheap and rapid to the UK at least.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 27, 2019, 06:49:53 pm
content: That's nice to know. And yeah I think I've also got good results with HK Post, unfortunately not many companies seem to offer it?Another option if you're not in a hurry and want it cheap is to use OSHPark. At least for over here, you can select a free shipping option, which goes through the postal services. Count about 3 weeks from order to delivery (yes it's a lot, but not that bad compared to some free or very low cost shipping options from China).

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2019, 07:27:24 pm
content: 1) Bare copper clad PCB for a ground plane.2) Deadbug ICs3) Air wires using thin, colored leads.4) Decoupling caps, pulldown resistors etc. directly soldered to the ground plane, like poles.5) Series resistors etc. directly soldered to the deadbugged component legsIf large non-GND planes are needed, make cuts to the ground plane copper clad using a Dremel like tool to isolate a section. Another option is to cut another piece and glue it on the top.I don't tend to use specialized SMD protoboards.

author: hagster
author_rank: Frequent Contributor
timestamp: July 27, 2019, 07:38:27 pm
content: Quote from: KE5FX on July 27, 2019, 11:32:13 amWe call this ’Dead-bug' style.Personally, if it's anything mor than a small test for a circuit sub-system, I prefer just getting a cheap PCB designed. I have seen some amazing dead bug builds, but they generally aren't very reproducible once the first batch of changes are made.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2019, 08:04:50 pm
content: < 50 total component legs: deadbug> 50 total component legs: design and order a PCB.> 50 total component legs, and you must have a proof of concept prototype finished tonight: deadbug, and good luck!Manual prototyping without a custom PCB is painfully slow, no matter what methods and tools you have. It's used when actual calendar time is more important than work hours. Otherwise, designing and ordering a PCB tends to be less painful.

author: ebastler
author_rank: Super Contributor
timestamp: July 27, 2019, 08:25:03 pm
content: Thanks all for the input so far! In summary, the recommendations seem to fall into three categories:SMD chips on DIP adapters, everything else on 0.1" perfboard using through-hole components. Fine for non-critical (low speed) circuits.Mount SMD ICs dead-bug style or with Kapton tape under the pins; solder wires (preferaly thin, enamelled) directly to the pins. Should allow for higher speed, due to shorter wires, SMD passives, and availability of a ground plane.Do a proper PCB layout right away.Surprisingly, no votes for dedicated SMD protoboards, unless I overlooked something. That's great information -- exactly the kind of practical feedback I was hoping for.Approach (1) is what I have mostly used so far. Sometimes I have used (3), but only when I felt reasonably sure of my design, and was hoping to actually use it in my project. So approach (2) is what I will try!I have a preference for the "sunny side up + Kapton tape" style, I think, rather than using dead-bug mounting. And while I see the point of a ground plane, I like holes and solder pads for the occasional though-hole component and connector. Come to think of it -- I used to have some plated-through perfboards with square pads on one side, and very small pads and a ground plane on the back. Haven't seen those in a while, but they must still be available?

author: magic
author_rank: Super Contributor
timestamp: July 27, 2019, 08:26:09 pm
content: Quote from: ebastler on July 27, 2019, 11:42:50 amThat's neat. I sometimes mount SMD passives and SOT23 transistors on normal perfboards similar way, it makes the circuit smaller than using THT stuff.0805 size is just right for mounting on 2.54mm pitch perfboard. 0603 works too. I prefer resistors in 0805 because markings are easily visible. I have good eyesight and can read that 0603 stuff, but 0805 really make it easier. Higher power too and less likely to get lost.OTOH, I have 100nF capacitors in every size down to 0201, for soldering directly to IC pins when power is next to ground.A quick and dirty option for simple one-off PCBs is to draw them by hand with a felt pen and etch.

author: Miti
author_rank: Super Contributor
timestamp: July 27, 2019, 10:09:19 pm
content: a) I always design the board and order it atwww.pcbway.com. At $5 for 10 pcs plus shipping you can't go wrong.b) For hand solder, I don't recommend going smaller than 0603. In the oven, 0402 is possible.c) I only hand solder the boards with very little parts count. You can order a cheap stencil together with the board. I love my toaster oven.d) Yes, forget TH. Dive into SMD and never look back.

author: tggzzz
author_rank: Super Contributor
timestamp: July 27, 2019, 11:09:46 pm
content: Quote from: ebastler on July 27, 2019, 08:25:03 pmSee the very usable techniques inhttps://entertaininghacks.wordpress.com/2020/07/22/prototyping-circuits-easy-cheap-fast-reliable-techniques/Note that they aren't used exclusively, but are used where beneficial and in conjunction with other techniques.

author: KL27x
author_rank: Super Contributor
timestamp: July 28, 2019, 01:08:29 am
content: QuoteI have not used electric eel's version, but I have tried my own version.There are major problems with this, in practice.Yes, you can bridge pads to make a circuit. You can even go out of your way to use as few jumperwires as possible. In some cases, you can even make simple circuits with zero wires, which can look great.The major problem is it is very difficult to debug. It is much easier to follow jumper wires than it is to see these solder tracks. When the empty pads are tinned (either factory plated or the fact they will inevitably get tinned during building/reworking), it is very difficult to follow half pitch (0.05") solder tracks with the naked eye. All you can see is a sea of tin/solder. And even under mag, where you can see perfectly, it's like being in the suburbs, looking for the tan house with the white fence. But all the houses are tan with a white fence, so you are constantly double-checking your row/column. When looking at a PCB, each trace has a unique shape and you have landmarks. Jumperwires, even if they are all the same color, each one has unique bends and angles and whatnot.I occasionally use a piece of 0.05" small piece of veroboard, mostly for hacking/adding one component to something. In practice this usually means cutting just a tiny piece barely bigger than the component, just to give a place to put an IC and add jumperwires and small passives. It's usually easier to make PCB for the starting point, and just use these stuffs for modifying that.

author: techman-001
author_rank: Frequent Contributor
timestamp: July 28, 2019, 02:06:42 am
content: Quote from: ebastler on July 27, 2019, 08:25:03 pmThis is a deadbug technique I'm experimenting with. I have more pictures and details on my doc page at:https://mecrisp-stellaris-folkdoc.sourceforge.io/prototyping.html#prototyping

author: tautech
author_rank: Super Contributor
timestamp: July 28, 2019, 02:34:51 am
content: Quote from: ebastler on July 27, 2019, 08:25:03 pmMaybe there's just not a good selection.Here's Dave's mailbag vid where he shows off a selection posted in:https://youtu.be/MwL3qgMNYLc?t=1743Quote from: Miti on July 27, 2019, 10:09:19 pmWell yes and no.You'll see jumpers used in modern SMD design when it's nuts to add another layer and so increase PCB cost when sometimes the use of a TH passive or 2 can open the routing pathways required so that even a jumper might not even be required. Otherwise to keep the design SMD get a selection of 1206 or 1210 passives to allow for a wider footprint to route traces under.Depends a bit on how much TH stuff you have and want to hold onto but if you're doing any repairs you really should hold onto your TH components.Each to their own I guess and I've found the occasional use of TH passives can restrict projects to just 1 or 2 layers.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 28, 2019, 10:19:40 am
content: as being notoriously too lazy laying out and etching pcbs, I use dremel drilled islands for Rs, Cs, and transistors, dead bug for DIP chips and TSSOP/LQFP adapter boards in every needed combination; however I'm avoiding BGAs so far since the wiring is somehow suspicious to me, but maybe I change my opinion if there'll be no alternative to such a chip.I do everything in that manner - from DC to lower GHz range

author: Siwastaja
author_rank: Super Contributor
timestamp: July 28, 2019, 10:34:26 am
content: The smallest TH resistors (with thinnest leads possible) are great for SMD bodges, because they double as a resistor and wire. Much quicker to solder than an SMD resistor, then a wire to it.But often you don't have small enough TH parts available.

author: poorchava
author_rank: Super Contributor
timestamp: July 29, 2019, 02:00:08 pm
content: In the company where i work we often have weird-shaped boards, so we can add protoboards on the waste areas of the panel. We literally have like 100kg of protoboards at hand.Privately, I use something similar to what Mike Harrison (mikeselectricstuff) is selling:http://www.whitewing.co.uk/protoboard.html

author: mark03
author_rank: Frequent Contributor
timestamp: July 29, 2019, 06:25:36 pm
content: Quote from: techman-001 on July 28, 2019, 02:06:42 amTempted to draw an analogy between this and programming in Forth, but I won'tSeriously, that is impressive. You have way more patience than I.On the main topic, I may be lucky, but I almost always prototype with a custom PCB and some common-sense measures like extra pads, etc. I can only think of one "coaster" I've made out of a couple dozen boards. It's the rare case that can't be reworked with some bodge wires and creativity.

author: ogden
author_rank: Super Contributor
timestamp: July 29, 2019, 08:28:38 pm
content: Quote from: mark03 on July 29, 2019, 06:25:36 pmLOLBuilding miniature ships in a bottle is another analogy that comes into mind. Someone who is doing deadbug for >200pin circuit that includes 0.5mm pitch chips, clearly do not value his time.

author: techman-001
author_rank: Frequent Contributor
timestamp: July 29, 2019, 08:36:47 pm
content: Quote from: mark03 on July 29, 2019, 06:25:36 pmHahahah, some real Forth humor at lastIt does require a 20 - 40 x microscope and steady hands ... but not that steady as I'm 65 years old.This is a experiment leading into much more interesting possibilities. For instance, BGA MCU's can be very cheap indeed compared to the leaded versions, in fact I paid $0.45 each for the STM32L053 chips in that picture. They have the memory below plus all the M0+ low power peripherals :­ 64 KB Flash memory with ECC­ 8KB RAM­ 2 KB of data EEPROM with ECC­ 20-byte backup registerJust because a tiny BGA chip has 64 pins doesn't mean one has to use or even connect to them all ;-)Imagine if one only needed 4 I/O's for a miniature project ?

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: July 30, 2019, 11:57:36 pm
content: I design usb scopes as a hobby for the development experience.My first design was 460K samples per second and all through hole.Once I got up to 2MHz samples I found I needed to use SMD TQFP 0.5mm pitch PIC microcontrollers but I kept the rest through hole for ease of building.My first attempt wasn't good as I bent a couple PIC pins being to rough and had to bin that attempt.On the next attempt I was more careful and got the PIC lined up as spot on as I could then applied some solder.I then put plenty of solder on the other 3 sides, way too much really.I then found with plenty of liquid flux and a copper braid I could remove most of the solder. I found the trick was t ohold braid on the pins and move soldering along the braid so it didn't bend pins.I put the PIC on its own small PCB that had through hole connectors to the motherboard.Through the connector pads I could buzz the pins out for adjacent shorts.In fact in some cases a short didn't matter as both pins were inputs and not used.I have built 3 pcb's now and they work great.

author: ludzinc
author_rank: Unknown
timestamp: August 02, 2019, 01:11:14 pm
content: Oh god that board is atrocious!

author: ebastler
author_rank: Super Contributor
timestamp: August 02, 2019, 03:05:15 pm
content: @ludzinc: Your comments comes across as judgmental and derogatory. It is also quite unhelpful since you don't say what is wrong with nigelwright's layout.Personally, I would route the tracks symmetrically and at 45° and 90° angles, but really that's mostly to satisfy my OCD. I am pretty sure the electrons will happily flow in arbitrary directions.And I would probably use SMD caps and quartz and place them on the bottom of the PCB, which avoids interference with the routing on the top and gets them closer to the processor chip. But since the adapter is meant to go onto a breadboard with further (longish?) external wires, we can assume that it is meant to work at clock rates where the exact placement of the caps is not critical.Are there other aspects of the layout one shoud be concerned about?

author: KL27x
author_rank: Super Contributor
timestamp: August 02, 2019, 10:23:58 pm
content: That wouldn't work very well on a breadboard. Gotta do SIP or DIP for breadboard. Quad pack, no good. this board is obviously for:QuoteThe only obvious things with this board, to me, are lack of ground plane and the trace width and routing. Trace width probably a mil or 2 smaller than necessary. And the arbitrary angles do not help with the PCB etch. The size of the gaps in the copper should not get too large compared to the trace size. I try to keep the gaps around a small trace to be roughly same thickness as the trace to maybe only 50% thicker. An easy way to fix this is to just use a top pour and set the gap/clearance as desired.Of course if you are only ordering a small amount, it doesn't matter. You pay based on a formula that doesn't include this stuff. The fab will obviously make extras and throw away the excess, including the ones that fail. At some point of high volume order, your fab might actually make suggestions to increase the yield. Tiny traces with large empty space around them tend to break when you etch the board.This might seem totally counterintuitive. You might think adding the top pour would near double the areas that could bridge and that the larger the clearances the better. But it's just not so. The areas right next to traces/pads is etched away, first, due to turbulence from the resist. Large empty spaces take the longest time to etch away, and during this time while waiting for them to clear, the traces are undercutting themselves.

author: Someone
author_rank: Super Contributor
timestamp: August 02, 2019, 11:49:20 pm
content: Quote from: ebastler on July 27, 2019, 08:25:03 pmThe SMD pitch prototype boards are great but only if you have chips matching their spacing, for more complex prototypes you quickly end up with more than one pin pitch and it gets hard to do anything other than dead bug. But they are still a great starting base:https://www.digikey.com/product-detail/en/vector-electronics/8021/V2017-ND/565946

author: Unixon
author_rank: Frequent Contributor
timestamp: August 03, 2019, 08:47:20 am
content: I would suggest to use a totally different approach to SMD vs TH.TH prototyping is efficient at component-level, while SMD prototyping is not, SMD becomes efficient at least at module-level.Therefore, it is much better to organize the entire workflow in a different way:1) Establish a continuous project queue/conveyor. Now you will have to design, assemble and test different boards at a time, forget about working on a single project.2) Design simple modules that include an IC and all requisite parts to get it working. Buy SMD-TH adapters where appropriate.3) Keep sending boards to manufacturing and don't rely on quick turnaround, just switch to next task.4) Assemble project from these self-sustaining modules, not raw parts, this is no longer the way.5) Think about a "standard" form-factor and interconnect for your modules.You will feel much more comfortable working with SMD when you'll have enough basic building blocks to assemble all you want and all design stages filled with sub-projects.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: August 03, 2019, 11:55:35 am
content: That pcb was routed pre making changes to my pcbcad software.The problem was "off grid" SMD pins.The software can now align track backwards to previous pin and forward to next pin.This gives a much cleaner layout.The pcb works absolutely fine at 200MHz, have three working systems.Most of the i/o signals are low speed anyway.The crystal and its caps and decoupling is close to the PIC on the pcb so thats major hurdles dealt with.After that the I/o is simply 3 lines to a 74hc4051 and the rest to power rails.

author: nali
author_rank: Frequent Contributor
timestamp: August 03, 2019, 12:40:02 pm
content: A bit of a mixture for me. Normally I'll go straight to PCB as proto PCBs are cheap or quick enough now (unfortunately never both!). Putting 0R resistors in signal lines can be pretty handy as they offer scoping points and breakout pads if something went wrong and you need to do some wire bodges.Anything I'm really not sure about I'll invest in a manufacturer's eval board.Also, for low speed breadboard these save the faff of soldering to adaptershttps://images.app.goo.gl/kAgmN6Xfw7uGsEcC9

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: August 04, 2019, 05:15:11 am
content: Quote from: nali on August 03, 2019, 12:40:02 pmI thought about using one of those but I needed decoupling and crystal right next to the processor.The processor runs at 200MHz so is fussy about decoupling.