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atmega8

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Joined: 19/11/2013
Location: Germany
Posts: 724

Posted: 10:15am 11 Aug 2015

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Hello,

in the past Days i have received some of Grog's MM+ Explore 64 Boards.
Very fine and accurate Boards, super job Grogster !!!

Soldering the 64 PIN PIC is not that difficult.
The hardest part is to align the pins of the controller with the pads on the board (for me).
This is the half job and the soldering is the easiest part for me.
I use solder sucking wick to get rid of the unwanted solder.

Do you have a "trick" how to align the PIC as exactly as possible?
I do this by hand with strong glasses...., but uahhhh

Any good tips for this?

THX

Dietmar

palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1992

Posted: 11:56am 11 Aug 2015

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You could try using a pair of self closing tweezers to hold the chip while you solder one of the corner pins to hold the chip in place. I bought a microscope and it has a spring loaded arm to do the job.
Paul.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 9603

Posted: 03:12pm 11 Aug 2015

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You really could benefit from a microscope, if you don't already have one, for this kind of tiny pin-pitch.

I put up a thread not so long ago with a link to an AmScope unit for a couple of hundred US bucks + freight - well worth the cash, if you are likely to be doing more then the one chip....

As you have worked out by now, alignment of the chip with the footprint is essential to get right, as you only have 0.5mm between pins, and 0.2mm between the actual pads on the PCB footprint - not much room at all for mis-alignment!

With my microscope, I can align one of these chips in about 5 seconds now, but that is only cos I have had some practise by this point.

I use tape.

Cut a thin length of sellotape or other(even PVC insulation tape would work fine), and gently press this down onto the chip while it is still in it's carrier - the chip will stick to the tape. Tape needs to be no wider then the black plastic pack of the TQFP chip itself.

Move the tape ends to the board - the chip will come with the tape, as it is stuck to it.

Align the chip by rotating and sliding the tape ends, to get the chip in perfect alignment with the footprint, then gently press the tape down onto the board.

Just pressing the tape down WILL cause a mis-alignment as the tape stretches - another reason I prefer sellotape, as it does not stretch like insulation tape can.

Triple-check the alignment, and adjust the position, by moving the tape ends, till you have perfect alignment.

Flux and solder the two diagonal corners of the chip which are accessible - don't worry about the tape covering two sides of pins for now.

Check again that alignment is still OK, and if it is, then solder all remaining pins on the sides of the chip that are exposed.

Remove the tape(gently!), and flux and solder the other two sides.

Clean with PCB solvent and anti-static brush to make it look nice and clean.

Check under microscope for any bridges.

All of that needs to be done with an anti-static strap on at all times, to protect the chip from any discharge.

I use 0.5mm 60/40 solder.
I don't bother with lead-free for SMD stuff, as lead-free needs a much higher temperature, whereas lead solder flows at a much lower temperature.

When applying solder to the iron tip, you only need a TINY amount - just enough to essentially "Wet" the iron tip. If you can see a solder blob on the tip, you have WAY too much solder. Just the small amount of solder is usually enough to solder ALL 16 pins on one side of the TQFP, with the help of flux.

I "In-and-out" solder these chips rather then drag-soldering, but you can do whatever works. Using in-and-out, I have not needed to use solder wick to soak up excess solder for any of the modules I have built this far.

Set your iron to about 250'C if you are losing your 0.5mm TQFP virginity, or if you are experienced soldering these chips, you can use 300'C or so, so long as you are quick with your soldering so as not to overheat the chip pins or board pads.

Hope that helps a little.

Smoke makes things work. When the smoke gets out, it stops!

WhiteWizzard
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Joined: 05/04/2013
Location: United Kingdom
Posts: 2934

Posted: 08:43pm 11 Aug 2015

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@atmega8

I simply put a blob of solder on a 'corner' pad (it doesn't matter if this blob shorts out a couple of pads). Then with the aid of a magnifier, I bring the chip to the pads with one hand (this hand also steadies the PCB on the worktop), and melt the solder blob with the iron in the other hand. To locate the chip is easy with a steady hand and a magnifier - you WILL need both!

Once the chip is in the correct place, remove the iron and examine alignment. If not quite correct, re-heat blob and reposition. I normally make two attempts at this - the first to get it 'almost' right, the second to get it exactly right. May sound like long way of doing things but as Grogster says, it only takes around five seconds.

Once the allignment is correct I then solder the 'opposite' corner pins to hold the chip down firm and then start on a third side (if TQFP) and solder all pads (shorting them all out), then fourth side, then back to first two sides. Then wick & flux to clean up. Total time less than a minute

There are many methods - it is a matter of personal choice which one you prefer. The best method is the one YOU are happy with that works!!

WWEdited by WhiteWizzard 2015-08-13

atmega8

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Joined: 19/11/2013
Location: Germany
Posts: 724

Posted: 03:33am 12 Aug 2015

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Hi,

thank you for all this practise tips..

I think it was not a good idea to pre-solder the pads on the board.
With all those solder buckles on the board, it is nearly impossible to align the chip.

Next time i will use a flux pen for better soldering.

What sort/manufacturer of flux pen can you recommend ?

THX
atmega8

MicroBlocks

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Joined: 12/05/2012
Location: Thailand
Posts: 2209

Posted: 03:58am 12 Aug 2015

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I tin the pads first with a very thin layer of solder. Then i tack 2 corners. The solder point just has a tiny little bit of solder.
Once it is 'fixed' in place with 2 corners tacked i load up the solder point with solder and drag it along the pins. The pretinning of the pads helps with the flow and 'pulling' the tin to the heel of the pin.
Then cleanup with solder wick.
All of the above with good amounts of flux.

Microblocks. Build with logic.

Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 9603

Posted: 04:25am 12 Aug 2015

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As Dave Jones says on his blog "And don't forget the flux - flux is everything!" - and it is.

I use gel flux in a syringe, but you can also use a liquid flux pen.
Electrolube make good products for this, but most electronics shops in your area should be able to sell you a flux pen or gel syringe for electronic rework.

I find that the PCB house I am using at the moment(Shenzhen2U) supply excellent HASL boards(hot air solder levelling), and as such, all the pads are already tinned with solder for you, so just place and go!

Boards from a few years ago did used to suffer with consistency of the HASL process, but the Shenzhen2U boards are excellent here, and never seem to have any left over solder blobs on the pads following the journey through the HASL process at the factory.

Not all PCB houses are the same though, so TZA's method is also good.

As WW said - no method is THE method to use - whatever works for you, I just posted what I do.

Smoke makes things work. When the smoke gets out, it stops!

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