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Is this possible?

So speaking of SMT....

Is this even possible to hand solder with a fine tip solder station and a magnifying lamp?
I'm looking for any tips before I attempt it.... I've only got 3 tries.

20150908_182519.jpg
Bosch BMP280 (labels wrong on circuit board)
 
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FWIW, I have found careful alignment, lots of flux, and a chisel tip to work best for such components, i.e. Drag soldering. You could consider gluing the component down first with a spot of superglue.
 
Should I pre-tin the pads or try to flow in solder?
I'm thinking moderatly generous pretin the board only and pre-flux the chip pads.
 
I'm NOT a SMT-soldering expert (total beginner) but that's a leadless package and it looks like the pads on your boards are barely larger than the pads on the device. I don't see how you're going to solder that with an iron, regardless of tip. If you had long pads that would let you put the iron on the pad NEXT TO the chip, I could see that having a chance (I think that's how Schmartboards are supposed to work, though they also have grooves in the pads to guide the solder and iron).

You might need to use a hot-air station or, really, the toaster-oven or skillet method, to solder those chips to those boards.

Or, try a new layout with extended pads (without solder mask on them) so you can tin enough of the pad that you can get the iron on the pad while the chip is sitting in the proper position. Fortunately that's only a couple bucks worth of OSHPark purple goodness.

Good luck.
 
I agree, I should have made the pads longer. As it is there is a only tiny bit of pad exposed after placing the chip.

I've also been considering the hot plate idea. Maybe a small aluminum plate an using my butane soldering iron with the hot air tip.

Using cyanoacralate is a great idea so the chip doesn't blow away if I go with hot air.
Must not glue over the pressure port however it will also be hard not to have the glue flow under the chip.

The three boards were only $0.95... but a two week turnaround.
 
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Tried hand soldering a microswitch with pads under the body. Couldn't make it work. Somehow you've got to get the heat between the pads on the board and the pads on the component. Somehow you'd like to inspect the work or check continuity, but without an x-ray machine, the only thing you can do is a functional test.

If you end up doing another PCB version and you absolutely positively have to hand solder, perhaps you could put tiny plated through holes on the PCB directly under the chip pads so you could solder from the back? Maybe even remove a little rectangle for interior castellated edges so that you'd be able to get make a solder fillet for each pin.
 
I think I'm going to try the hot plate method first.
I don't have any really good flux other than a Kester flux pen left over from making some solar arrays.
I ordered some Chip Quik tack flux and will try to pre-tin the pads, then place the chip and hope for the best.
 
I've solder dozens of the BMP280 (and others) onto OSHPark pc boards. I recommend low-temperature solder paste (ChipQuik) I don't like SRA or other brands. I also recommend a combination hot plate (although this by itself will work) and hot air gun. I use this rework station and highly recommend it. You get a lot of extra junk with it but the hot plate/hot air gun combo is worth twice the price. MEMs sensors don't like heat so using low-temperature solder paste treats them well, and rework is easy when you find (and you will) that you have solder bridges or cold joints. Once you get the hang of using this system you will be able to design with and assemble fine pitch (0.4 mm) QFN, LGA, and even BGA components with ease.

One thing I notice on your board is there doesn't seem to be any provision for bypass caps on the VDIO or VDD lines. You really need 100 nF XR5 or better bypass caps for these sensors to get reasonable quality data. Also, I am assuming you will have the I2C lines pulled up elsewhere, but it is convenient to have pullups on the board itself, especially for testing or long lines. I use 4K7 but 2K2 work well also.

Oh sorry, just noticed it is set up for SPI!

One last thing, generally placing traces directly underneath MEMS sensors is a no-no. GND traces are slightly less bad, (and I have done exactly this when space is tight) but i would recommend that you keep the top layer copper free underneath the package if possible.
 
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Thanks everyone for all the great tips!
I just ordered the ChipQuik low temp solder paste. I'll let you know how it goes when it arrives.
This seems like the best option for success. I don't plan to use a stencil and hopefully I'll have a steady hand that day.
Can you wipe off, clean up and retry with the solder paste prior to heating if you goof on the application?
I also ordered some 1206 SMD Resistor, Capacitor and LED kits from Aliexpress for future projects.

Since this was my first attempt with Eagle and Osh-Park, I intended to keep it simple and use external breadboard components.
The breakout just brings out all 8 the BMP280 pads, so I should have both I2C or SPI options available.
I made a few mistakes on the board labels (this is why I shouldn't muck around with stuff at 2:00AM)
I also ordered some 1206 SMD Resistor, Capacitor and LED kits from China for future projects.

I should have chosen a larger device for my first project.
Here's my second Osh-Park board design that I just received today.
20150909_211202.jpg
It's a breakout for an ESP8266-13 wifi module... Definitely a much less challenging solder task.
 
Last (maybe!) piece of advice: get some of these. 25 Gauge is the best I've found for fine work meaning 0.4 mm pitch and 0402 passives. I use 25 Ga for everything now. For the ginormous 1206 passives you ordered you could just use a paint brush! Or a shovel!

But yes, the paste wipes away easily with a paper towel. Very easy to use. Application onto the pads is a bit of an art but with practice you'll find out what works well. You could also get some isopropyl alcohol to clean up flux residue but this is really optional.

You can also, reheat, remove soldered components, clean off the solder with a copper wick, clean the pcb with alcohol and start all over again. Or anywhere in between.
 
Haha
I originally ordered SMD 0805 sized components, but after fretting over the BMP280 I decided to be a little less "adventuresome" and go with the gianormous 1206's!
 
I also note that there is a new stencil service in town, OSH Stencils (they appear to be separate from OSH Park, the PCB fab). I have yet to use them, but the pricing is came out to about ½ of the OSH PCB fab for a trial run I did. For such a low price, I'd check them out. For small SMD parts that have little to nothing exposed re: pads, a stencil is a great solution - even the hot air station can be made to work with it, as long as the underlying components are glued down.
 
On the subject of gluing:

For hand soldering with an iron this might be necessary or at least beneficial. I've never tried it. But for solder reflow with hot air/plate methods, I would advise against it.

A large part of the art of proper assembly is component placement. The great thing about solder reflow is the components want to line up with the pads, and no matter how careful you are in placing the components (and you should take the care to be as close as you can, 5x lighted magnification works wonders here) you will be off. But the reflow process will automagically align the components in most cases for the best fit and least stress. The latter is important for MEMS sensors, and rigidly gluing the components in all but the exact minimum stress location (nearly impossible) will deliver less than ideal results.
 
onehorse,
I'm curious,
For your pesky products, are you hand placing components, or using automated assembly?
 
Last (maybe!) piece of advice: get some of these. 25 Gauge is the best I've found for fine work meaning 0.4 mm pitch and 0402 passives. I use 25 Ga for everything now. For the ginormous 1206 passives you ordered you could just use a paint brush! Or a shovel!

But yes, the paste wipes away easily with a paper towel. Very easy to use. Application onto the pads is a bit of an art but with practice you'll find out what works well. You could also get some isopropyl alcohol to clean up flux residue but this is really optional.

You can also, reheat, remove soldered components, clean off the solder with a copper wick, clean the pcb with alcohol and start all over again. Or anywhere in between.

Do you use a compressed air applicator or just use a syringe by hand?
I find using the syringe hard to control (paste keeps coming out even after you stop applying pressure to syringe plunger). and for smaller needle size, it is almost impossible to get the paste out.
I just use the tip of a jumper wire to apply the paste. a bit hard for small pitch pads, so I might try stencils next time.
 
Do you use a compressed air applicator or just use a syringe by hand?

I have learned to control the flow of the syringe by hand. It can be tedious and time consuming to do so, and it's an art to be sure.

I can assemble 2 - 3 boards per hour depending on the complexity. But after much practice, the yields are near 100%. The economics could be improved with machine assembly methods but I sell at such low volumes that hand assembly still makes sense.

I am experimenting now with having boards made and components assembled in China. I can get 4-layer boards made in lots of 100 for just a little over the component cost. This is a great deal and will free up a lot of my time previously taken up with hand assembly, especially for relatively large volume sellers like battery chargers where the margins are low but the assembly time is high.

Although I recommend hand assembly for prototyping and just for the pure pleasure of taking something you designed from concept to tangible, working reality yourself (with a little help from OSH Park and Mouser, of course!).
 
So after some major postal delays, I finally got the Chip Quik Low temp solder paste.
Actually I got two tubes as the first one was lost in the mail for about 2 weeks... the lost one and the replacement arrived on the same day.

So following onehorse's advice, I managed, on the first try, to solder my Bosch BMP280 SMD pressure sensor correctly, and it's working on the breadboard.

  • I dabbed the paste on the printed circuit board pads with a sewing needle tip.
  • Placed the component with tweezers on the board.
  • Placed the board on a thin aluminum plate.
  • Heated the plate with a butane soldering iron with the hot air jet attachment.

While watching with a magnifying lamp, it was amazing how the tiny component pulled into place on the board once correct temperature was reached.
I scorched the edge of the board trying to clean up one little droplet.

Here's a image of some 0805 and 1206 tiny components, including the 8 pin BMP280, a photo of the soldered component, and a plot of the data.
EPSONScan000228b.jpg EPSONScan000228c.jpg EPSONScan000229.jpg Capture.JPG

Thanks everyone for the great tips and advice!!
 
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Congratulations and well done!

Don't forget to close up the solder paste tightly with the provided caps on both ends. I store mine in the fridge when not in use. Lasts longer with these precautions.

Next stop: 0.4-mm pitch, 48-pin QFNs!
 
I second using the syringes for storage and use. I've found that tubs of solder paste have a tendency to separate like organic peanut butter. That in turn leads to inconsistent stenciling.
 
A loosely related question. What do you do with old solder paste ?
I've got some left that is almost two years old now and I guess the volatile parts of the resins are evaporated, leaving a very stiff mixture that is fbecoming too stiff to stencil, let alone squeezing it through a small needle on a syringe.

How do you dispose of this stuff when it's not usable anymore ?
Or can the shelf life be extended by some means ?
 
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