Introduction: How to Neatly Solder (without Loads of Wires!) Decoupling Caps on SMT Microcontrollers.

Picture of How to Neatly Solder (without Loads of Wires!) Decoupling Caps on SMT Microcontrollers.

This instructable is written to teach you how to use a neat and tidy method of prototyping with SMT microcontrollers (or other devices) on an adaptor board.

After struggling to make a neat job of effectively decoupling the power pins on my PIC18F I decided something needed to be done!

This instructable shows what I did.....

This is my first instructable (I thought it was time to give something back!) so go easy on the comments ;-)

S.

The first picture (below) shows the completed board - looks neat (apart from the burnt flux!) doesn't it....read on!

Step 1: Lets Begin...

Picture of Lets Begin...

The first step is to solder your device onto the adaptor board as can be seen in picture below.
I find that the best way to solder these fine (ish) pitch devices is to use plenty of good flux and some leaded solder (dont tell the environment though ;-) !).

Step 2: Copper Tape and Capacitor Lead Forming.

Picture of Copper Tape and Capacitor Lead Forming.

First you need to cut a ~20mm x ~20mm piece of copper tape and stick it to the centre of the underside of the adaptor board.
Next you need to poke the capacitor legs through the adaptor board with one capacitor leg placed through the positive supply (to be decoupled) hole and the other leg placed through the ground pin connection. This is fairly easy with the PIC18F since the power and ground connections are usually close together.
Next you need to solder small pieces of solid core wire onto the ground legs of each cap as shown in the images below. These pieces of wire then need to be formed such that they overlap the copper tape in the centre. This copper tape will become our makeshift ground plane.

Step 3: Soldering the Decoupling Capacitors.

Picture of Soldering the Decoupling Capacitors.

Once you have formed the solid core wire over the copper tape you need to then carefully solder the wire to the tape. This is best done quickly and with minimal solder.
The image below shows the soldered connections.

Step 4: Insulating the Negative Plane.

Picture of Insulating the Negative Plane.

The next step is to deal with the positive connections.
First you need to insulate the existing copper tape 'ground plane' with some tape. I used Sellotape but i am sure there is something more suitable! Maybe Kapton tape?
Make sure that the ground is well insulated and then move on.
Next you need to stick another similar sized piece of copper tape over the insulated ground plane.
The image below shows the ground plane insulated with Sellotape.

Step 5: Add the Positive Plane.

Picture of Add the Positive Plane.

Once you are happy that the ground plane is well insulated you should stick the second piece of copper tape onto it as shown in the images below.
Make sure you get the copper tape well stuck down!

Step 6: More Capacitor Lead Forming!

Picture of More Capacitor Lead Forming!

Next you need to take some more single cored wire and solder one end to the positive side of the decoupling capacitor and the other should be formed such that it is over the copper tape. This copper tape is to become our positive 'power plane'.
See images below for an idea of how it should look!

Step 7: A Bit More Soldering.

Picture of A Bit More Soldering.

Now you need to solder these positive connections.
Again, make sure you make a neat job of the soldering and don't use too much solder.
If you look close you can see the Sellotape just poking out from the edges of the copper tape.
See image below :-)

Step 8: Connecting the Supply Wires.

Picture of Connecting the Supply Wires.

Next you need to take some red and black wires and solder the black one to the ground connection on the top side of the adaptor board and the red one to an adjacent positive connection.
See image below for details.

Step 9: Making Sure You Haven't Shorted the Whole Thing Out :-)

Picture of Making Sure You Haven't Shorted the Whole Thing Out :-)

Next you need to use a DMM (Digital Multi Meter) to make sure you have not shorted the ground connections to the positive connections. If they are shorted you are in big trouble since this connection method (with tape etc) is not easily re-workable!
The DMM (set to Ohms measurement) should show open circuit between the red and black wires if all is connected correctly.
See image below showing what a working board should show on the DMM.

Once it works you have a nice, reusable board suitable for prototyping and showing off to people without heaps of wires etc.

The finished article 'should' provide decent decoupling of the supply pins and will show some of the benefits of using a ground and power plane although the capacitance between the two copper 'plates' is likely to only be a few nF (nano-Farads) at best.

If you liked this instructable and have an interest in electronics please pop over to PCBPolice and say hello :-)

Many thanks,

S.

Comments

est83 (author)2017-05-03

You have been source of great inspiration. I am doing a project with a PIC24 and I have chosen a DIP version because I am not familiar using SMD components. Anyway I could not mount it on a prototyping board because the connections to the decoupling capacitors were too long and the PIC was resetting continuously. When I soldered to a perf board the problem was solved. I found myself at short of pins and I noticed a bigger brother of the PIC I am using has more pins in a SMD package but I have found that the SMD adaptors have long distance from the PIN to a place suitable to mount a capacitor.. With your idea I can now try to prototype with SMD PIC !

TheWaddleWaaddle (author)2011-09-04

I hate to be the one correcting the Grammar Nazi, but your suggestion is incorrect. If you remove the parenthesized words, it spells the 100% gramatically accurate sentence of "How to neatly solder decoupling caps on SMT microcontrollers.", rather than your suggested "How to solder neatly decoupling caps on SMT microcontrollers.", unless he is using a special form of decoupling capacitors called "neatly's" which I have yet to hear about. You could also add the parenthesized words at the end of the sentence, which would read "How to neatly solder decoupling caps on SMT microcontrollers without loads of wires!", which is still 100% gramatically correct... Now I feel like the Grammar Nazi :-(

-TheWaddleWaaddle

I posted this more than a year ago, and I have since then learned a bit more about grammar. I saw that I was wrong a little while ago, but never really cared to take the comment down.

ciroman (author)M4industries2012-01-28

And thus you got owned for posting a comment before thinking it through. Good job.

omnibot (author)2009-04-30

Good ible. Also I have the same multimeter.

ste5442 (author)omnibot2009-04-30

Thanks!
The DMM is actually pretty good for the price - DMMs are usually only used for indication only and not for accurate absolute measurements so I dont care if the measurement accuracy is 1% or 5%.
Ballpark is fine in most instances (for me anyhow!).

S.

PCBPolice

omnibot (author)ste54422009-05-02

Same here. Been thinking of getting something a bit better later on but currently it's all I need.

rachel (author)2009-04-29

This is super clear about how... but as a fairly new electronics hobbyist, I'm not at all clear about Why. What's a decoupling capacitor and why do you need them on smd components?

osgeld (author)rachel2009-04-30

i suggest you read this

http://en.wikipedia.org/wiki/Decoupling_capacitor

it basically acts as a noise suppressor

ste5442 (author)osgeld2009-04-30

Eeeeeexactly ;-)

S.

PCBPolice

Whatnot (author)2009-04-30

Copper tape eh, yeah I'll get some at the copper-tape emporium on the corner.

ste5442 (author)Whatnot2009-04-30

Oh, but dont buy it from a garden centre - they charge a lot for it. Grab some from Farnell, RS, DigiKey etc ;-)

S.

PCBPolice

ste5442 (author)Whatnot2009-04-30

Most garden centres sell it for the top of plantpots - apparently it keeps slugs off them!

S.

PCBPolice

osgeld (author)2009-04-29

very handy trick, and it does look nice and neat thanks for sharing!

ste5442 (author)osgeld2009-04-30

Thanks Osgeld!

S.

PCBPolice

ste5442 (author)2009-04-29

Hi All,

Please note that although this method looks nice it does also have some advantages over wiring each decoupling capacitor seperately (which is what you have to do with these adaptor boards normally).
Using this method you obtain a nice low-impedance ground connection for your decoupling capacitance. If you were to use wires for each ground connection you are effectively adding inductance (and resistance) to the ground leg of each decoupling capacitor - this adds to the capacitor ESR and reduces its effectiveness.
Inadequate decoupling can cause all kinds of strange behaviour so when grounding decoupling capacitors its best to use nice, low impedance traces ;-)

S.

PCBPolice

jeff-o (author)ste54422009-04-29

Shame they didn't just slap a ground plane on the back of the PCB for this purpose! For an even more rugged solution you could glue a thin piece of PCB to the back instead of the copper foil.

ste5442 (author)jeff-o2009-04-30

The cost saving from switching to a single sided copper PCB (with non-PTH's) from a double sided, PTH PCB means they can make the boards for much less than half the price. But yes, it would have been nice of them to do that ;-)

S.

PCBPolice

jeff-o (author)2009-04-29

You forgot to mention that a decent soldering iron is also required. Something with a nice fine tip and ideally temperature control.

ste5442 (author)jeff-o2009-04-29

I agree, a decent iron is something everyone (who is into electronics) should own. Many cheap irons are simply too hot and totally unusable with small surface mount devices.
To save your sanity and your components it is best to make the investment in a decent iron with a nice tip and at least some level of temp control.
A very capable iron can be bought for less than £100 or even less from eBay. Second hand irons from eBay should not be ruled out since you can always buy new tips - the heating element, PSU and handle are pretty rugged and should last well.
If your pockets are bulging with cash why not check out an iron from Metcal :-)

S.

PCBPolice

jeff-o (author)ste54422009-04-29

Mmmmm, Metcal are nice - we have them where I work. Also lots of nice Hakko stuff. I'm spoiled! All this nice stuff makes it hard to go back to my $40 Weller at home...

osgeld (author)jeff-o2009-04-29

we have Hakko's at work, i get home and look very mad at my radio shack el cheapo, hoping one day it will morph but after after a decade with that RS i can work some magic with it, but its still tricky

ste5442 (author)osgeld2009-04-30

Hi Jeff-o and Osgeld,

I know how you both feel - I have a cheap no-brand Maplin iron which was about £25. It does have a temp control but it ranges from 'blast furnace' to 'surface of the sun'! Also, nobody sells any small tips for it :-(
But....I do get by with it very well and regularly solder 0402 devices with it without any tears :-)

S.

PCBPolice

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