Surface mount soldering failed! Why?

I have a small board with my project that I thought I'd make smaller by surface mount soldering some components. I picked the larges SMT components I could find, and soldered them by hand. However, the circuit does not work. I verified each component has a good connection, but the resistors and capacitors all read out slightly incorrect values (these are 1% devices!). Is there a trick to this that I'm missing?

Is your DMM a .1% accurate device? that would be a minimum requirement for accurate measurements.
Did you verify your circuit line by line and component by component?.
Did you verify power and ground connections?.
Do you realize that my Crystal Ball is broken?
Did you post it here so someone else might help you?.
Did you attempt to describe purpose and behavior of the non working circuit so someone might offer an opinion or solution?.
Did you really expect any help when you've offered no information about that which you desire help with???
Do you do this often?

Doc

Your Kung-Fu is not strong.

Did you know that measuring resistances and capacitances "in circuit" is a futile effort?

Have you calculated what the actual resistance should be at that point in the circuit, taking into account all the other components that are also connected to that part of the circuit?

Have you ever heard of Mr Thevanin?

It sometimes helps to put the board on a hotplate at ~260C degrees and give it a slight jiggle once the solder has melted.
Reconnects dry joints.

I'm not looking for anyone to troubleshoot a circuit, I'm looking for general advice from people who have hand soldered SMT components - hence my question "Is there a trick to this that I'm missing?".

Come on people, I expected better from you. Attacking the OP is not productive. If you have nothing constructive to say, stop wasting electrons.

lemming - thanks, your post was helpful.

EDIT ATTACK?, NO ONE here has ATTACKED YOU and you've had "suggestions" from me as well as Majenko AND a GOOD one from Lemming... EDIT
It is also a requirement that the board be clean too, Unless you have an undiscovered circuit fault (Very likely) or a defective component (unlikely).
It's probably a good possibility that you didn't check your circuit before you made the board and If you are using a 'working' board someone else made...
You failed to place the components properly... or as you suggest all the soldering is bad and you've not found the last part improperly soldered.
Patience is a virtue and as many will confirm here you can't check your own work too much or often.
I can't tell you of the number of times I've done a PCB and my employer has asked me to re-check it, before I learned that I make mistakes on the BEST of day's
It's a drag to have to "Fix" 100 PCB's which was all we would make until the whole device was tested properly and found working in all respects.

Doc

Ultimately only electrons can sense a dry-joint or a short, so a multmeter looking for shorts and open circuits is the definitive way to test, but before doing that again I strongly suggest getting a good magnifier out and doing a careful visual inspection of the board. Look for dry joints, solder bridging, damage to the components.

Also if you can narrow down which part of the circuit is defective by detective work it might save time. Are the power rails shorted? Is the circuit drawing too much or too little current? Can you trace a signal through it step by step?

If you didn't clean the board carefully prior to soldering its possible that some of the pads haven't wetted at all due to oxide film (this is true for both copper and tin surfaces) - it takes a magnifying glass to verify this. It also helps to remove the flux with a flux-cleaner first - easier to see things then.

There is no particular trick to hand soldering the larger SMD components, although as for any soldering, the PCB needs to be clean. It also helps to either tin the pads or wipe a no-clean flux pen over them before you place the components on them. If you want more help then you'll need to post a photo of your board and a schematic, and describe what is not working.

SMD Soldering Tutorial

To state the most important SMD soldering technique 1 more time... mentioned above.

Did you use a boatload of FLUX? If not, I say that was likely part of your problem.

I use a very liquid water soluble flux ( and highly active) and flood the board with it before soldering begins.

Yup, lots of flux is your friend. Find a no clean version. I still use 90% isopropyl wipes afterwards to clean it off though.

Also, proper tip shape on the soldering iron is very important for drag soldering. As is a light touch on the pins themselves as tight pin pitches = thin pins = easy deformation. (ie 0.5mm and below)

Alligator: Let's assume that your SMT soldering is "adequate." Why do you think that it is the SMT soldering that has failed? Does the same board work when assembled with non-SMT components? Does that mean that the PCB itself is not designed for SMT components? You do know that an SMT resistor that says "1000" is NOT 1000 ohms, right? The not-quite-matching meter readings are probably explained by trying to measure "in circuit", and shouldn't be anything to worry about. (that said, since SMT components are smaller, they can be more easily damaged by too much heat at too high a temperature from a soldering iron.)

AS I SAID BEFORE...!

It is also a requirement that the board be clean too, Unless you have an undiscovered circuit fault (Very likely) or a defective component (unlikely).

Doc

With plenty of flux you can solder the most delicate of components with the cheapest of equipment.

I use a cheap 30W soldering iron, and "budget" lead free solder. And gallons of flux.

I solder 0.4mm pitch 100-pin TQFP chips on a regular basis, on home-made PCBs with no solder mask.

No problems.

It's all down to the flux.

If you think you have enough flux, then you probably don't.

Add more until the board is literally swimming in flux. Then add more :wink:

Use "No Clean" flux in a pen - it's the most convenient. And use some Isopropyl Alcohol to clean it off - even though it's "No-Clean" I still find it leaves a sticky residue behind.

Yup, I love flux too. When in doubt, add more, especially if you need to rework a pin or two. Lots of flux ensures a nice shiny connection and happy electrons make my day.

Totally not trying to hijack this thread, but where is a good place to get good no-clean flux like you guys are talking about? It might help the OP and others!

Thanks!

Any major electronics retailer.

e.g., RS, Farnell (Newark), Rapid, Mouser, Digikey, etc.

Techni-Tool

I thought I would post my first SMD experiment... Using toner transfer method and home etching.

Yes, it worked. Flux to the rescue...

Very good.

Here's a couple of my recent ones, all done with the TT method, on double-sided FR4 - the second one has components on both sides too.

WaveProPrototype.jpg