![]() It might seem like a lot of work to put in before making any boards, but this couple of days getting everything in a row will save you time when it comes to populating the boards, and will in turn result in better quality final prototypes. Some last-minute overnight ordering was in order, followed by collation steps for those parts. The numbered bag of components was then placed in the appropriate hanging file for its line number, and the process was repeated with the next line number and so on until the whole BoM was covered.Īt the end of the component collation, we had a box of hanging files containing numbered component lines, and inevitably there were a few lines which either weren’t quite right or hadn’t arrived. ![]() Its line number from the spreadsheet was written on the label, and the spreadsheet was updated to show that it was present. Every line on the BoM spreadsheet was checked, that the component was present, was it compatible with the package it should be on the board, and was it present in sufficient numbers to populate the boards. Each hanging file was labeled with a range of numbers corresponding to BoM lines, so 1 – 5, 6 -10, 11 – 15, and so on to the end of the BoM. We started with a storage box of the type designed to hold hanging files. The hanging file box we used, a Really Useful Product. It’s necessary to both ensure that everything has arrived and is the right component for the job, and to index and array them in a form such as to make the placement on the boards as easy as possible. There began the second major task, that of collation. In the days running up to the build, a variety of packages arrived containing the components. So this step became an involved trawl through an array of suppliers for the elusive parts, sometimes ringing company reps to beg a few free samples. If your design consists entirely of generic components that every supplier has by the reel then sourcing is as simple as making the order, but sadly very few real designs are like that. It stands to reason that the complexity of component sourcing increases with the number of individual component lines in the BoM. The story didn’t start on the build day, instead a few weeks ago the Bill Of Materials, or BoM, was exported from the CAD package, and the task of sourcing all the components began. So there we were, setting out to make a batch of eight prototype PCBs. Setting up a pick-and-place for a very large job is a performance in itself, and for a very small run of boards there is a hard financial decision to make over whether it is justified. The answer to that isn’t really mine to give as the boards weren’t commissioned by me, but in reality it’s a nuanced decision based on a combination of cost, number of boards, and the eventual customer’s deadline for a trade show. Would we be insane to use a pick-and-place machine for this job, or are we insane not to have used one? Peripitus, via Wikimedia Commons.Some of you reading this will now be asking “What on earth are you doing making this run of boards by hand, you should be doing it with a pick-and-place machine, or you should be hiring a specialist company!”. Apologies then, any pictures will be rather generic. I can’t describe the board in question because it is a commercially sensitive prototype for the industrial customer of the friend I was putting in the day’s work for, but it’s worth going through the minutiae of successfully assembling a small batch of prototypes at this level. I was hand-stuffing a row of large high-density boards with components ranging from 0402 passives to large QFPs and everything else in between. This is being written the morning after a marathon session encompassing all of the working day and half of the night. It’s a process that requires care and attention, but it’s fairly straightforward once mastered and we can create small runs of high quality boards.īut what about the same process at a professional level, what do you do when your board isn’t a matchbox-sized panel from OSH Park with less than 50 or so parts but a densely-packed multilayer board about the size of a small tablet computer and with many hundreds of parts? In theory the same process of screen print and pick and place applies, but in practice to achieve a succesful result a lot more care and planning has to go into the process. We take one or two boards, screen print a layer of solder paste on the pads by using a stencil, and place our surface-mount components with a pair of tweezers before putting them in the oven. We’re used to reflow soldering of our PCBs at the hacker level, for quite a few years people have been reflowing with toaster ovens, skillets, and similar pieces of domestic equipment and equipping them with temperature controllers and timers.
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