1206 SMD hand soldering pad size

Hello,

I'm currently working on a PCB designed to control an 8x8x8 LED cube.
So far i planned to used thru-hole components but over the last week in tried to shrink to board more and more (the original intention was to save cost at the manufacturer, but in fact it really is my perfectionism that strives for the smallest feasible size).
Today it thought about replacing thru-hole with SMD components, primarily resistors, to increase the compactness.

The first picture shows the driver stage for the cube levels (anodes) via MOSFETs.
The 150 ohm gate resitor and the 2,2k pullup take up quite a bit of room and I want to replace them with SMD resistors.

Since I haven't soldered SMD before I'm planning to go for 1206 size.
Therefore I changed the package type to a standard 1206 eagle footprint and the parts came out as shown here:

Here I'm wondering about the pad size and the fact that more then half of the pad is below the component. I get that from reflow with solderpaste this is probably useful and space saving, but I'm wondering if this is also the best way for hand soldering with a soldering iron.

Therefore the question: Is this SMD pad configuration useful for hand soldering or should I look for bigger pads, or pads that are moved a little bit more outwards, respectively?

Best regards,
dumbel

Hi,

I've done hand soldering with both very thin solder and also solder paste.

The biggest problem with using an iron on those small parts is holding the part down when you lift the solder tip. The solder sticks to both the part and the iron tip, so when you lift the tip often the whole part comes up with it and stays on the end of the tip instead of the board. This means you have to have a way to hold the small parts down while you hand solder. If you can do that you are good to go. I even used Elmers glue a couple times before soldering giving it plenty of time to dry first :slight_smile:

With the heat gun the little parts stay there pretty well with gentle air flow, and the solder paste melts and distributes nicely.

1206 is ~12X6 mils easily hand solderable.
I have used 1210 for 1206

.

A method I have used often is to apply solder to the pad which will be way too much, so I use a solder wick to remove the excess solder. Then I place the part, hold it down with a wood toothpick and apply heat to each joint. If necessary add a little more solder to provide a nice fillet and strong joint. If you don't have any solder wick you can use finely stranded wire loosely twisted together and dipped in soldering flux.

Thank you for all your answers so far.
But i have the feeling that the main point of the question was not really addressed so far.

Primarily I was wondering about the pad size and position (mostly located under the part). The way the pad is shown in eagle I have a hard time imagining to be able to contact and head the pad with a soldering iron when the part is on the pad.

I would like to keep the pads as they are in order to save space if that's possible, but if it is advisable to move them a little further out in order to hand solder them, I would do so. For that i would like to get some recommendations or experiences from your projects.

Best regards,
dumbel

I have a board made with Eagle which uses 1206 pads.
The pads easily accommodate a 1206 SMD device and have room for soldering by hand.

.

Best electronics investment I ever made was a £25 toaster oven, slightly modified to
reflow oven, very very neat results, like magic. (Modification was to move the lower
heater element to the top).

Hi,
If I make PCBs the one thing I keep in mind is SERVICEABILITY , someday, probably the first time I try it, I will have to change something, or a component will fail.

The number of PCBs I find that are UNSERVICEABLE because of the quest to make it SMALL, is increasing in the commercial world.

So make your PCBs so you can work on them when it comes to component replacement and trouble shooting.

You may want to put a CRO or DMM probe somewhere, make room for it, be generous with TEST POINTS on your PCB.
GND Test point
Vcc or Batt+ Test point
Any voltage regulator output Test Point
Any signal output Test Point
All a Test Point needs to be is a solder pad.

An indicator LED to show when the PCB is powered up, if you want low power put a cuttable/removable jumper link in series with the LED.

Don’t try and make it look completely like the commercial guys.

I repair PCB’s, usually without circuit diagrams, the inclusion of labeled test points can cut the repair time in half.

Tom… :slight_smile:
PS So endeth the lessom “my basic philosophy on PCB design”.

You can rework SMT boards with hot-air rework station - not unservicable, I've replaced 4 chips on
one small board that I blew up successfully.

You do need the right tool for the job, and the right tool is not a soldering iron.

Hi,

The number of PCBs I find that are UNSERVICEABLE because of the quest to make it SMALL, is increasing in the commercial world.

The manufacturer in the bit to get it small has custom made large scale integrated ICs or custom programmed control ICs.
Replacement IC's not available cos its OEM and 24 months old, obsolete, and they want you to update to newer model.
Or uses multilayered PCBs that somewhere develop an open circuit and short circuit to other tracks. Thus letting the smoke out.

Tom... :slight_smile: .

Normally, I would not like something where there were SMD parts literally underneath another part - in this case, though, you can bend the legs on the TO-220 package, so the two resistors are still accessible...

I mirror almost all of LarryD's comments..

  • 1206 are hand solderable.
  • I too invested in a $17.00 (USD) toaster oven from my local wal-mart..

** ^^that coupled with a Silhouette Cameo vinyl cutter.... I have not spent any money on getting stencils made for my project, nor having to have someone else assemble for me either.

Super clean, professional looking boards!!

All boards/projects I have made using my cheapier toaster oven:



(board on left is custom board, compared to Uno & Shield)

Hi,
Have you used Ohms Law and checked the power dissipation in the smaller SMD components?

Tom.... :slight_smile:

I normally hand-solder 0805 parts and I also have done 0603 parts. They can share each other's pads. An 0805 part on an 0603 pad isn't very happy and it's not a saleable product but it does work. 0603 goes on to 0805 pads nicely.

The images of the part footprints you are seeing in Eagle are just a representation. It's not exactly that size. Just put down the pads in the manufacturer's recommended places and it will totally work. For standard size resistors, there's no need to even check the datasheets.

Adafruit sell a couple of nice 'books' of SMD parts. Buy the 0805 book and also a blank book to store all your specialised parts in.

Once you start soldering SMD with a stencil, then you will start avoiding through-hole parts and favoring SMD everywhere. I would try to do your board with all components SMD, except the connectors. When you see the parts magically align themselves to their correct places on the board, you will be hooked on this contsruction method.