You can do your personal Surface Mount Technology primarily based PCB meeting with only a handful of instruments and a few endurance. At the guts of my SMT course of is stopping to examine the varied steps all whereas attempting to keep up a little bit of cleanliness within the course of.

Surface mount or Surface Mount Technology (SMT) is the fashionable approach to assemble Printed Circuit Boards (PCB) and is what is usually seen when opening a contemporary piece of tech. It’s a lot smaller than the older Through-Hole (TH) expertise the place the part leads have been inserted into holes in PCB, and act we known as “stuffing” since we needed to stuff the parts into the holes.

A number of specialised instruments make this rather a lot simpler, however resourceful hackers will be capable of pull collectively a solder paste stencil jig, vacuum tweezers, and a modified toaster oven with a controller that may observe the reflow profile of the solder paste. Where you shouldn’t skimp is on the standard, age, and storage of the solder paste itself.

Join me after the break for my video overview of the method I exploit in my workshop, together with particulars of each step of my SMT meeting course of.

Component Size Matters

Surface mount bundle names is usually a little bit complicated. In the video I discuss pats which have a pin pitch of 0.5 millimeters, however in terms of resistors, we use numbers like 0603 and 0402 which measure 0.06×0.03 inches. It’s at all times to good concept to have examples you possibly can reference to make sure you’re utilizing the fitting dimension bundle.

Adafruit Ruler Showing 0603 Size

Looking at my trusty Adafruit ruler with part sizes proven I’ll say that I generally do the 0603 dimension parts frequently, although I’ve achieved 0402 for RF parts the place much less dimension means much less issues like inductance which combat you as you go up in frequency. I don’t work with the smaller 0201 parts as I’m afraid of inhaling them they’re so small.

Pretty a lot all the SOIC elements you see could be achieved utilizing the strategies I present within the video and I generally go all the way down to 0.5 mm lead spacing, although within the video I solder some chips which have 0.4 mm lead spacing, the smallest I do in my house lab.

Caring for Solder Paste

Nowadays we “place” a part on PCB’s with out the necessity of holes for the parts leads, and as a substitute of making use of solder after the actual fact in its molten type, we use a solder paste consisting of flux and solder. The paste could be packaged in quite a lot of methods however I purchase my paste in syringes and I preserve them in a small fridge and just for a restricted period of time as solder paste has a shelf life relying on the type and the place you purchase it.

Solder paste is denoted by the flux that it’s primarily based on, I exploit “no clean” which implies just about what it says, the tip result’s operable with out cleansing the PCB. If I’m delivering the board to another person I usually clear it in any case which I am going over within the video.

Solder paste proven magnified X10

The solder is an amalgam of little beads of solder held in suspension with flux and could be the touchiest factor about DIY soldering because the solder has a particular shelf lifetime of weeks if not days relying on the producer. Simply put when you don’t keep in mind whenever you bought your solder, throw it away. I purchase a solder formulated for higher shelf life named Zeph paste which retains longer than a manufacturing combine, and I retailer it in a small devoted fridge (assume six-pack cooler) and saved upright in syringes with the needle pointed down.

Solder additionally is available in many varieties, beginning with leaded vs non-leaded after which variations relying on what sort of flux it accommodates. I exploit the “no clean” model which doesn’t have to be cleaned, or could be cleaned with alcohol as a substitute of the stronger flux cleaners.

Applying the Solder

Solder Paste Stencil with out Frame
Solder Paste Stencil with Frame in a Stencil Holder

There are a number of methods to get the solder paste on the PCB; it may be manually utilized utilizing a syringe and good outdated trend squeezing to deposit the solder onto the connector pads of the PCB. I even have an air stress operated dispenser that I don’t actually use.

My go-to technique is to make use of a paste masks stencil and squeegee the paste onto the PCB as seen within the video. There is a trick to squeegeeing the paste to not press too onerous whereas forcing the paste by means of the paste masks display. Paste masks stencils can be found for just a few {dollars} from the identical sources I purchase my PCB’s at, for bigger runs I might have a look at firms like OSH Stencil.

Inspect Your Paste, then Place Components

I at all times examine the PCB earlier than inserting the parts on the board and I exploit a stereo X10 microscope for this step. What I’m in search of is something that may create a solder brief later, I.E. if its shorted now it’ll more than likely be shorted later.

Manual Pickup Tool

The trick is to put parts on the board, form of snuggled into the solder paste actually, with out smearing the paste or bending the part leads. Tweezers work for smaller parts like resistors and capacitors however usually for Integrated Circuits (ICs) one should be cautious to put the bundle flat. I’ve quite a lot of methods to do that utilizing suction together with the little suction cup with a squeeze bulb for a totally guide technique or when doing rather a lot I may be impressed to fireplace up my little suction powered elements picker-upper made out of an outdated aquarium pump.

At Last, the Oven

I’ve tried quite a lot of reflow ovens together with the T-962 (full with mods per the Hackaday articles on the topic) however at all times discovered it wanting, particularly with tall, darkish parts because the radiation patter contained in the oven is considerably uneven.

In order to make a greater small scale oven I began with a Black & Decker convection oven and acquired the Controleo3 oven controller which comes with an auxiliary heating component to spice up efficiency. After making use of numerous reflective tape and excessive temp RTV the oven is sealed towards as a lot warmth loss as possible. The oven controller takes an hour for it to study the oven’s traits however as soon as discovered I received actually good and repeatable outcomes.

Home Reflow Oven

An essential consideration is the Solder Profile which is a chart of warmth vs. time. It is just about the alternative of simply sticking the boards in a sizzling oven till the solder melts, which is just about assured to simply bake off the flux leaving little clumps of solder versus the graceful reflow that we wish to obtain. The Solder Profile takes care of assorted phases resembling preheat and speedy cooling along with the precise reflow stage.

I put in an extra heating component on my oven. The Controleo3 calibrates itself to the oven and even the dimensions of what the oven is loaded with. I re-train the oven if doing massive PCB’s utilizing a clean board.

Final Inspection

True to my nature I slap the ultimate soldered merchandise beneath the microscope one final time and look rigorously at every lead noting any solder bridges or voids within the course of. I’m additionally in search of the solder to have melted completely and never look “grapey” or the place the solder might have coalesced into tiny clumps as a substitute of a correctly whetted solder joint.

.4mm Leads Soldered in Home Lab Magnified X10

I like to offer the boards a visit by means of my ultrasonic cleaner that I preserve only for PCBs. While not normally essential it provides the boards a pleasant skilled look and makes inspection simpler.

Conclusion

Hopefully one can see that doing DIY SMT meeting is definitely potential and may even be achieved for small scale manufacturing. In my case I can solder parts all the way down to 0.4mm lead pitch which is fairly small so long as I do ample inspection. Keep it clear, preserve your solder paste recent, and examine at each step and also you’ll get nice leads to your personal workshop.