Let's build a couple of uO_c's!

dComposerdComposer Contributor, Member

I've been active on the NYMS discord for a bit now but I'm still pretty new to this forum so I thought a fun introduction would be to start a DIY thread acting as a soup-to-nuts chronicling of a couple of uO_c's I'm gearing up to build once all the parts arrive!

The sense I'm getting from members I've talked to so far is that there is an apprehension to start smd projects... but once you get over the tiny size it's *so much easier than building through hole projects*! Lets treat this like an AMA / build blog so feel free to jump in with questions!

Also, I should mention that I'm just a hobbyist and have no formal EE training or anything so caveat emptor :D

Comments

  • dComposerdComposer Contributor, Member

    Ok, so while I'm waiting (im)patiently for the parts to arrive, lets catch up:

    I received the pcbs as a trade but I didn't have any panels so I went to jakplugg's GitHub and downloaded them: https://github.com/jakplugg/uO_c

    The panel is hiding in the cleverly titled "panel" directory. The files I needed were in the "PCBpanel_JM" subfolder. Going into that folder you see a bunch of files that have extensions that begin with "g". These are "gerber" files -- that's the standard file type that fab houses like to receive and they tell them where to drill or what to silk screen on which layer.

    Wikipedia explains it more elegantly:

    The Gerber format is an open ASCII vector format for printed circuit board (PCB) designs.[1] It is the de facto standardused by PCB industry software to describe the printed circuit board images: copper layers, solder mask, legend, drill data, etc.

    Anyway, I digress... Usually once you produce all the gerbers you need you then zip them all up into one file and that's what you send to the fab company. This is the "panel.zip" file that's in the director so all I had to do was grab that and send it off to my favorite fab house: https://jlcpcb.com/

    Once you sign up for an account, you click on "quote now" and you're magically whisked away to a new page that has a button that lets you upload your gerbers (panel.zip). Once this happens, a bunch of the fields in the order form are automatically filled out for you (like the dimensions and panel thickness) and defaults are chosen for you (like pcb color and surface type).

    The surface type is kind of confusing so here's the difference (lazily pasted from wikipedia again):

    HASL:

    HASL or hot air solder leveling is a type of finish used on printed circuit boards (PCBs). The PCB is typically dipped into a bath of molten solder so that all exposed copper surfaces are covered by solder. Excess solder is removed by passing the PCB between hot air knives.

    ENIG:

    Electroless nickel immersion gold (ENIG) is a type of surface plating used for printed circuit boards. It consists of an electroless nickel plating covered with a thin layer of immersion gold, which protects the nickel from oxidation.

    HASL is fine but just note that you want to get the lead-free HASL for panels because you don't want to have to worry about lead poisoning while wiggling! I use leaded HASL for my pcbs since I use lead solder but for the panels I use either lead-free HASL or ENIG. For this build I chose the slightly more expensive ENIG because the gold will look cool on the panel. And looking cool is all that really matters, right? I'll post pics of the panels once I get them!

    Anyway, that's it for the panels! They ended up costing me $23 but keep in mind the minimum order is x5 so that's a pretty nice price!

    Here are all the options I ended up selecting for this process:

    Gerber file: uO_c_panel

    Build Time: 2 days

    Layers: 2

    Dimension: 40mm*129mm

    PCB Qty: 5

    PCB Thickness: 1.6

    Impedance: no 

    PCB Color: Black

    Surface Finish: ENIG-RoHS

    Copper Weight: 1

    Gold Fingers: No

    Material Details: FR4-Standard Tg 130-140C

    Panel By JLCPCB: No

    Flying Probe Test:Fully Test

    Castellated Holes:no

    Remove Order Number:Yes

  • mrwilliammrwilliam Mod
    edited January 20

    For me personally, the only DIY experience I have is kits where all boards, panels, components, knobs, etc are included.

    Is all of that included with with project or did you have to source everything? If you had to source everything, could you walk us through that process?

  • dComposerdComposer Contributor, Member

    Absolutely nothing is included in this project! But it's way better that way. You'll see that going this route is great because you have total control over exactly which brand and source of components you use / what your panel looks like / which knobs you use /etc. Also, instead of getting a big-ole-unorganized-bag-of-components in a kit (what's up with that? Some kits I got just had a pile of components floating around the bottom of the box that would take me a day and a half to organize!), Mouser/Digikey/whatever sends each component in its own little drug baggie. It's so much nicer! I'll go over sourcing components from the BOM in the next mega-post.

  • dComposerdComposer Contributor, Member

    Ok! So lets go over sourcing components from the BOM in this next mega-post!

    First off, terminology: BOM == "Bill of Materials"... aka the big ole spreadsheet that tells you exactly how many 10k resistors you need and where to place them on the pcb.

    The BOM for uO_c is saved on Google Sheets here: Google sheets BOM

    Notice that rows 3-10 list all the capacitors you'll need, 12-22 are all the resistors, and then all the IC's/etc are below. This is the usual layout for BOMs and it's nice for keeping things organized. I like to export this file using File -> Download and then saving it locally. This is because the google sheet doc is read only and I like to color code the rows so I know which ones I placed an order for, which ones I already have in a box somewhere, which ones I already placed on the pcb, etc.

    The columns headers should be intuitive enough. There's a couple of nuances that aren't readily apparent though. If this is your first time soldering SMD components, note that they come in various sizes. From largest to smallest (that you'll normally encounter in eurorack modules) the sizes are:

    • 1206
    • 0805
    • 0603
    • 0402

    Refer to the size chart attached (again, lazily copied from wikipedia) below to see the differences in the sizes.

    Note: while most "scientificy" stuff uses metric measurements, for whatever reason, these size codes are imperial measurements. This is annoying because 0603 and 0402 show up in both and if you order the metric version you'll end up with like subatomic particles! If you do this, know that you're in good company. I think this is just a mistake you have to make in the sourcing side quest in order to level up your sDIY character. Anyway, this code is kind of hidden in column C "Name" where you see all the _0805 and _1206 suffixes to the names.

    Another nuance to note is the quantity column (column A). There will be many times when you'll only need like quantity 3 but, when you're ordering the components from Mouser or Digikey, oftentimes it's much cheaper to order 10 or even 100 components than just the 3 or 4 the BOM states. This inevitably leads to you having a box of unsorted extra components under your desk that you place great value in when you have like 1 component left in finishing up a future build but you're missing that one final bit that either you forgot to order or disappeared in an unfortunate tweezing accident.

    Also, notice column E lists all the suggested mouser codes for the listed components, but these will oftentimes not be available when you begin your build so you'll have to make your peace with the "search similar" section at the bottom of the component page listed on Mouser or Digikey. Resistor replacements are easy peasy: 9 times out of 10 you basically just need to match the resistance and size (imperial not metric!), but be sure to double check the "Notes" column (column G in this BOM) to see if there are any other things you need to look forward to. For resistors, if it's not specified then 1/4 watt power rating and 5% tolerance are usually fine. Notice the 0.10% notes in rows 14, 18, and 22 though -- they're referring to the fact that these resistors need a 0.1% tolerance.

    Capacitors are a bit more nuanced. You need to find a replacement that has the same:

    • capacitance
    • same or higher voltage rating
    • case code - in (this is the size code in inches!)
    • dielectric

    IC's and the rest of the components are a bit trickier since they are all different so what I do when I can't source the originally linked mouser number is to just click the check boxes on the "search similar" section until it whittles the results down to 2 or 3. Then I open the datasheet of the original component in one window and the datasheets of the substitution options in another window and check to see if they look the same (ie, the pins all match up & the IC's characteristics look similar). A lot of times you'll find like 3 of the same components listed in mouser and one of them will be out of stock but that's just because they all come in different types of packaging and each type of packaging has it's own mouser code!

    I think that's it! One final thing to note is that once you add a component to your mouser cart you'll have a box called "Customer #" that you're allowed to put whatever text you want! So if you really want, you could list, say, "R16, R18, R20, R22, R24, R28, R32, R36" in the customer # spot for your 33k resistors and you'll get that printed on your little drug baggie of 33k resistors! Pretty cool trick...

    I think that's about all there is to know about sourcing components but if you have any questions please ask!

  • dComposerdComposer Contributor, Member

    Oooh! Speak of the devil - look what UPS just delivered!


  • dComposerdComposer Contributor, Member

    Ok! So you got your pcb, you got your components -- now you have to populate your board and solder everything in. Easy! This is the part of the build where you crank up a podcast and let the lead-based solder-zen commence. There are a few methods to soldering smd components:

    1. heat up some regular run-of-the-mill solder on one pad with your soldering iron, place the component with tweezers and reheat the solder while holding the component down (or reheat the solder with your iron and gently slide the component in place). Finish up by soldering in the other side of the component. Easy!
    2. Buy some solder paste, apply a tiny, tiny, tiny, TINY bit to both pads and then place the component. Use a heat gun to melt the solder. Even easier!
    3. Same as #2 but apply solder paste to all the pads and then place all the components. Once every component is placed then literally plop it on your kitchen stove or a hot plate for like 8 minutes on high to melt the solder.

    Which method you choose is completely up to you. Some methods are better for extremely large boards (like #1 or #2) or if your board only has like 10 smd components (#1); but usually I prefer #3 because it's the fastest. And it's the easiest. It's so easy that it's almost like an arts and crafts project, except in the end you don't end up with bedazzled rhinestone bling -- you end up with a fully functional module!

    What you need for method #3 is:

    Passives are super easy since you just need to squirt a microscopic dollop of paste on each pad and gently place the component on top with your tweezers. IC's are a bit tougher. Here's the technique I use: still try to use as little paste as possible on each pad but don't worry about bridges at this point. We'll fix those later. It's just a fact of life with this method but I feel like it's well worth the effort. The main thing to worry about at this stage of the game is that each IC leg is exactly lined up with its pad. Once you have everything lined up, put it on the aluminum plate and put that on your stove or hot plate. Some people even use an old toaster oven for this part. Crank up the heat and it takes about 8 minutes before the solder melts and turns a shiny silver. Also, at this point, glorious CAPILLARY MAGIC happens and all your components should pull themselves onto the pads. It's a sight to behold! Sometimes one side of a resistor/capacitor will heat up before the other side gets a chance to and it will tombstone. When this happens, I like to just gently nudge it over with my tweezers as quickly as possible (if feasible) or just fix it up during my "fix it up" next step.

    After everything cools, the "fix it up" step commences. You will inevitably have a few bridged IC legs. IT IS OK! Grab some flux and solder wick and wick those bridges into submission. As a rule, I like to hit all my IC's with some flux just to make sure no blobs of paste are hiding behind my IC legs and it just cleans up the area really nicely. If the pads are long enough, you'll be able to draw out the excess solder from the legs just with the heat of your soldering iron. The final stage of the "fix it up" stage is to grab a bunch of q-tips and some 99% isopropyl rubbing alcohol and clean all the excess flux off the board. It's important to clean up everything now before placing the pots and jacks because isopropyl rubbing alcohol will destroy the plastic on jacks and innards of pots so you won't be able to do this as easily later in the game. Another technique is to fill up the bottom of an old tupperware container with rubbing alcohol, plop the pcb in the bottom and use a toothbrush to brush all that flux off.

    Ok! That's enough for right now! Until next time...

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