Hand solderable 1GHz ARM Cortex A8 in TQFP package

http://olimex.wordpress.com/2012/04/24/cortex-a8-in-tqfp-sure-allwinner-a13/

by nabilt • 14 years ago

55 23 14 years ago

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obtino• 14 years ago

I don't know what kind of person would try to solder this by hand! It's a surface mount package. I wouldn't go near one without specialised equipment!

officialchicken2• 14 years ago

It's a QFP, not a BGA. Go get yourself a magnifying lamp, some solder braid, and some paste. It's really not that hard (unless you're soldering a lot).

femto• 14 years ago

Yep. Eminently hand solderable. Surface mount is self aligning, in that all you have to do is heat things up, apply the right amount of solder and the surface tension of the molten solder does the rest, making sure the solder goes in the right places. The key is that everything must be spotlessly clean, so the surface tension of the solder is not disturbed by contaminants.

In the absence of a hot air of infrared source, use a flat chisel tip about 3mm wide and fine solder to do a QFP.

Align the QFP on the pads. Alignment is crucial, since by not heating all pins at once you lose the self aligning of packages aspect of the surface mount process. Maybe tack diagonally opposite pins with a little solder, or lightly hold it in position. If you are right handed, have the iron in your right hand and solder in your left. Have one side of the QFP facing you. Start at the left hand corner and (if you are right handed), sweep from left to right, keeping the flat chisel in contact with the part of the pins, trailing across so it is in contact with the pads. Simultaneously feed the solder into the junction of the pins and iron with your left. It takes some practise to get the speed of the sweep and the rate of solder feed correct, so getting the correct temperature and amount of solder. Get it right and it takes a couple of seconds to solder one side of a QFP, with a single sweep. Turn the board 90 degrees and repeat for the other three sides.

If you get solder bridges, reheat, maybe using a little flux or removing some solder if there is two much. If things are clean and there isn't too much solder, surface tension will "magically" pull the solder from the bridge back onto the pins.

I've used the above technique down to 0.5mm pitch.

serialx• 14 years ago

It's definitely more hand-solderable than a ball-mount package. The latter one is basically impossible to solder using a tip.

Brashman• 14 years ago

I've done surface mount with a Radioshack soldering iron, solder, and some solder wick. It takes patience, but definitely doable.

(Side note: Essentially had to be able to solder surface mount packages to pass a class in college.)

nrp• 14 years ago

It's actually pretty simple to hand solder a TQFP by drag soldering. The key is to use plenty of flux and have solder braid handy to take care of any bridges. http://www.youtube.com/watch?feature=player_detailpage&v...

It's sort of a moot point with this Cortex A8 IC though, because the RAM it needs only exists in a BGA package.

Palomides• 14 years ago

way easier and quite cheap: just use a hotplate and solder paste ($30 hotplate, $5 solder paste)

officialchicken2• 14 years ago

Yes! And toaster ovens work well. Get some high-temp red spray paint too, so that the hotplate/toaster oven is clearly marked and never ends up in a kitchen.

regomodo• 14 years ago

Don't even need a hotplate. Any soldering iron will a concave tip, lots of flux & a touch of solder. Takes 4 strokes/drags and some extra flux afterwards to remove bridges (usually the 1st 2 pins on each drag).

It's surprisingly easy and i've had no issues on up to tqfp144's.

mbell2• 14 years ago

> I don't know what kind of person would try to solder this by hand! It's a surface mount package. I wouldn't go near one without specialised equipment!

Its actually very easy to solder packages like this and you really don't need paste. Paste is faster and results in less eye strain if your doing a bunch of them, just use a stencil for the paste application (which you can get easily and cheaply online).

The biggest mistake most people make when trying to solder things is thinking they need to do 1 pin at a time. Unless your talking huge pins (DIP-8) you don't want to do this. It is actually worse for the chip going pin by pin, you end up heating it up more and for a longer time.

Instead apply flux to the board, position the chip then "tag" opposite corner pins with solder to hold the chip in place. From there add more flux to the pins and use very fine solder (this is key) + a fairly fat solder tip, like a 1/4" chisel, just drag it down the each side of the chip while applying enough solder to suck onto the pins. You can do the entire chip in about 60 seconds.

Chips that actually suck to hand solder are things like QFN, PLCC (with small pads), and anything with a center pad (especially if its a thermal connection to the ground plane). You can hand solder such packages but its a serious pain and really can only be done correctly with a hot plate and hot air station. Small parts suck also, 0402/0201 or smaller resistors or caps are not fun to do without without paste + reflow.

EDIT: I should add that land pattern makes a big difference too. High density land patterns are much more difficult to solder correctly without paste + hot air or reflow.

marssaxman• 14 years ago

It's not as hard as it looks. What I do is stick the chip in place with tape, then tack down pins on opposite corners, then remove the tape and just go at it like crazy, letting the pins bridge as they will. Once it's all done and there's solder everywhere, I go back over it with solder braid to suck up the excess. A magnifying glass is nice but you can totally just do it by hand. Just embrace the mess!

aortega• 14 years ago

You can solder this by hand with a solder gun and solder paste, hardly specialised equipment. Thanks to the chinese guys that did this you can now hand-solder a computer that runs a modern OS like Ubuntu 12, you couldn't do that since the 70s.

sp332• 14 years ago

Wait, so A10 is a Cortex A8 plus other hardware? And the A13 is a stripped-down A10? Who names these things?

__alexs2• 14 years ago

And the (Apple) A5 is an A9. I think we need a chart :(

Gussy• 14 years ago

As someone pointed out in the comments these processors require DDR3 memory, which is only available (currently) in BGA packages. This means you can't quite use a soldering iron to build your own small computer, yet.

The real advantage here is not the savings in the soldering soldering but the savings in PCB complexity and cost. A small BGA with a few hundred pins will need at least 6 or more layers to be able to "break-out" all the pins from underneath the chip. With the TQFP package, all the pins are already at the edge of the chip, so it's possible to use a 4 layer PCB.

It's an exciting time when more people can have access build thing using this level of hardware. Now the next thing we need is decent documentation to go with these chips.

mbell2• 14 years ago

Honestly the price differential is very small between 4 and 6 layers now-a-days. In mass pro that is, they will still charge a solid premium for 6 layer at many quick turn / small batch PCB manufacturers.

The biggest savings comes from avoiding blind and buried vias which are still expensive to use but often required for dense BGAs. You can also usually get away with a larger minimum feature size (trace width) with a QFP which can also be a nice cost savings in the PCB construction.

robomartin4• 14 years ago

Soldering BGA packages "by hand" isn't really that hard. I've done lots of that. I placed it in quotes because, well, it really isn't done by hand ball-by-ball of course. All you need is suitable magnifier or inspection microscope, a stencil, solder paste, a temperature probe and a hot plate or toaster over.

  - Apply the paste to the PCB using the stencil
  - Carefully place all the components using the magnifier 
    and appropriate tweezers or vacuum pickup pencils
  - Place in the oven or hot plate
  - Carefully ramp up and down the temperature as required

I've built many high-speed (200MHz to 1.6GHz logic) prototype boards this way. Not the most fun and time-consuming but definitely do-able.

nabilt• 14 years ago

I was excited by this chip because like others have mentioned it reduces the tolerances and therefore cost of PCBs, which is great for hobbyists. What are the specs for your BGA boards and how much do they cost for small runs?

robomartin4• 14 years ago

The specs wouldn't be any different than they would be for a good quality board for TQFP with a pitch in the order of 0.5mm. If you need to support DDR3 (as the A10 does) and high speeds you need a good board anyway in order to make sure that the transmission lines remain true to design parameters. In other words, signal integrity is a concern with these designs and you just can't use a dirt-cheap board. It doesn't matter that the A10 is hand-solderable. You still need to attend to signal and power integrity and that means that a certain class of board is required.

Having done boards with FPGA's as large as 1152 balls (definitely not soldered by hand) I can tell you that good board houses produce good product and the difference wouldn't be much, if any between a controlled-impedance board for an A10 project versus an equivalent-sized BGA device.

This is important, so I'll repeat it: The A10 requires a controlled-impedance board.

EDIT: Just learned that the A10 requires DDR3. So BGA's are the order or the day. Hand-soldering with a soldering iron is simply not a reality for such a board. If you want to assemble one yourself you have to use a stencil and an oven or hot plate for reflow. Not that hard for small quantities.

I should also note that I've only done this when absolutely necessary. It makes a lot more sense to pay to have SMT boards assembled. It's not that expensive and assembly shops have all of the right equipment to get it right. With BGA's you really need to have full inspection (including X-Ray) in order to ensure proper attachment. This is particularly true in the case of high-speed boards.

__alexs2• 14 years ago

"It's not hard, you just need hundreds of dollars in equipment and some practice!" Sounds like "hard" to me.

TQFP can be done with common and cheap items like a cheap soldering iron, a flux pen, some copper wick and a pair of tweezers.

Symmetry• 14 years ago

Yup, flux is great, under appreciated stuff. First you apply the flux to the area you'll be soldering, then you put just enough solder onto your iron and drag it along the pins. The evaporating flux will pull the solder onto the pads. The hard part is in judging the right amount of solder to use.

robomartin4• 14 years ago

C'mon now, anyone seriously into electronics --even as a hobby-- ought to own more than a cheap soldering iron, a flux pen, copper wick and a pair of tweezers. A toaster oven is, what, $30? Yes, you have to get a prototype stencil made. These are also cheap. Google it.

Here's someone who wrote about the proposed approach: http://www.instructables.com/id/Toaster-Oven-Reflow-Solderin...

Hand solderable 1GHz ARM Cortex A8 in TQFP package

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