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'[EE] soldering TQFP packages'
2007\02\14@154940 by Bob J.

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Hi All, I just received some boards I designed to be used with a 24F.  The
24F is in a TQFP-64 package, and I haven't soldered anything yet with pins
that small.  I have a Metcal soldering iron with the hoof tips, I may be
able to do it but I think I may have better success with the "reflow
skillet" method of smt soldering.  Can anyone tell me where I can buy a
small serving of solder paste?  The standard syringe of Kester solder paste
from Digkey is 35 grams, which cost $42.00 and then you have the plunger and
dispensing tips on top of that.  The dispensing tips are $31.33 for a
package of 50.  With shipping I am looking at $75.00 for just the solder
paste, seems steep for a a one-off project, and the solder paste will go bad
before I will need it for a future project.

Regards,
Bob

2007\02\14@161647 by Herbert Graf

flavicon
face
On Wed, 2007-02-14 at 15:49 -0500, Bob J. wrote:
> Hi All, I just received some boards I designed to be used with a 24F.  The
> 24F is in a TQFP-64 package, and I haven't soldered anything yet with pins
> that small.  I have a Metcal soldering iron with the hoof tips, I may be
> able to do it but I think I may have better success with the "reflow
> skillet" method of smt soldering.  Can anyone tell me where I can buy a
> small serving of solder paste?  The standard syringe of Kester solder paste
> from Digkey is 35 grams, which cost $42.00 and then you have the plunger and
> dispensing tips on top of that.  The dispensing tips are $31.33 for a
> package of 50.  With shipping I am looking at $75.00 for just the solder
> paste, seems steep for a a one-off project, and the solder paste will go bad
> before I will need it for a future project.

Buy some solder wick and use the iron, it's not to difficult to do.

TTYL

2007\02\14@163348 by Tobias Gogolin

picon face
The question and solution is surface tension of the tin
Make sure you only have fresh tin on the tip
when it oxidizes its surface tension is bad
How is the PCB? Plate the contacts first with tin without the chip
then roll with plenty of tin the fresh solder over the placed chips contacts
let the extra tin roll and drop off with gravity (board vertical)
then you may not even need solder wick!



On 2/14/07, Herbert Graf <spam_OUTmailinglist3TakeThisOuTspamfarcite.net> wrote:
{Quote hidden}

> -

2007\02\14@182926 by Peter Todd

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On Wed, Feb 14, 2007 at 03:49:38PM -0500, Bob J. wrote:
> Hi All, I just received some boards I designed to be used with a 24F.  The
> 24F is in a TQFP-64 package, and I haven't soldered anything yet with pins
> that small.  I have a Metcal soldering iron with the hoof tips, I may be
> able to do it but I think I may have better success with the "reflow
> skillet" method of smt soldering.  Can anyone tell me where I can buy a
> small serving of solder paste?  The standard syringe of Kester solder paste
> from Digkey is 35 grams, which cost $42.00 and then you have the plunger and
> dispensing tips on top of that.  The dispensing tips are $31.33 for a
> package of 50.  With shipping I am looking at $75.00 for just the solder
> paste, seems steep for a a one-off project, and the solder paste will go bad
> before I will need it for a future project.

I bought some solder paste for a project a good year and a half ago...
Still seems to work just fine for hand soldering. I know they say it
goes bad very quickly, but I think that's for large mass production
applications where the exact properties are very critical. I know my
paste seems more runny than it did when I bought it, and for the
single dot application method those syringes are designed for that would
be a killer.

Heck, I haven't even been storing mine refrigerated like you are
supposed too.

--
http://www.petertodd.ca

2007\02\14@190028 by David VanHorn

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>
> Buy some solder wick and use the iron, it's not to difficult to do.


Ditto, just did this with some AVR parts.

Check the side of the pads, you may need to scrape gently with an xacto
blade to get a clean surface.  As usual, solder two opposite corners and
then verify alignment before doing any side.

2007\02\15@132344 by alan smith

picon face
I wouldnt tin the board first...it should already be.  And you will have a hard time getting the chip to sit flat while trying to tack the corners down.  Once you have it aligned (thats the nightmare usually) and bump it to make sure it won't move on you then just run a bead of solder up and down the sides and wick up the excess.  Once you do a few, you will find they are really not that bad do to. Even the fine pitch ones.  If you have a microscope it makes it easier, but at least an eye loop to inspect for bridges and opens after.  Remember you dont need lots of solder.  If you ever have a chance to look close at a board thats been flowed you can get a good idea of what you need.

Tobias Gogolin <.....usertogoKILLspamspam@spam@gmail.com> wrote:  The question and solution is surface tension of the tin
Make sure you only have fresh tin on the tip
when it oxidizes its surface tension is bad
How is the PCB? Plate the contacts first with tin without the chip
then roll with plenty of tin the fresh solder over the placed chips contacts
let the extra tin roll and drop off with gravity (board vertical)
then you may not even need solder wick!



On 2/14/07, Herbert Graf wrote:
{Quote hidden}

> -

2007\02\15@164110 by James Nick Sears

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face
To second all of this, I really hardly ever do a project without a  
QFP on it anymore and you can do it.  I usually don't do the covering  
all the pins technique, but tend to try to keep the joints separate  
and only wick the solder if I make a mistake.  Get a magnifier, I  
like the plastic pull down head mounted type.

Use lots of flux (I like the flux pens, and personally water clean  
with the compatible solder) and be aware of the temperature of the  
chip.  If it gets too hot to touch, you need to move onto something  
else and let it cool down.  Also, I like to jump around the chip a  
bit as I solder (or wick) to keep any one portion of the chip from  
getting any hotter then necessary.

One final tip: You don't want the iron too hot, but then again the  
point is to get the pin-pad interface hot, and the way to do that  
without having to heat the whole chip to soldering is with a  
sufficiently hot iron and an exceptionally clean tip.

-n.


On Feb 15, 2007, at 1:23 PM, alan smith wrote:

{Quote hidden}

>> --

2007\02\17@154821 by Dave Lag

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Herbert Graf wrote:

> Buy some solder wick and use the iron, it's not to difficult to do.
>
> TTYL

Speaking of SMTs,
After getting worked over by the local electronics shops I went
searching for a better source for Donegan Opi-Visors and lenses.

Turns out TowerHobby (.com) has an excellent selection and good prices,
about half what I paid locally.





2007\02\18@233927 by Charles Craft

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After many years of being a self taught (= good days and bad days) solderer I finally got a book on the subject:
      Quality Hand Soldering & Circuit Board Repair (Paperback) by H. Ted Smith (Author)

He recommends chemical cleaning of boards before soldering them but gives no specific chemicals.
I supposed if you assemble soon after receiving boards from the board house it's not an issue.
But I've been doing a lot of the Velleman kits for holiday presents and it looks some of them
have been on the shelf many moons before I got them.

Anyone done chemical cleaning of boards to remove the oxide before soldering?

thanks
chuckc


{Original Message removed}

2007\02\19@102627 by Marcel Duchamp

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Charles Craft wrote:
> After many years of being a self taught (= good days and bad days) solderer I finally got a book on the subject:
>        Quality Hand Soldering & Circuit Board Repair (Paperback) by H. Ted Smith (Author)
>
> He recommends chemical cleaning of boards before soldering them but gives no specific chemicals.
> I supposed if you assemble soon after receiving boards from the board house it's not an issue.
> But I've been doing a lot of the Velleman kits for holiday presents and it looks some of them
> have been on the shelf many moons before I got them.
>
> Anyone done chemical cleaning of boards to remove the oxide before soldering?
>
> thanks
> chuckc
>
Chemicals to clean pcb's? Try water and kitchen cleanser powder applied
with something like Scotch-Brite pads and elbow grease.

2007\02\19@112701 by Charles Craft

picon face

>>
>> Anyone done chemical cleaning of boards to remove the oxide before soldering?
>>
>> thanks
>> chuckc
>>
>Chemicals to clean pcb's? Try water and kitchen cleanser powder applied
>with something like Scotch-Brite pads and elbow grease.
>

I've had good luck with those pads on boards that didn't have solder mask or silk screen.

Have you used it on boards with either/both of those?


2007\02\19@120415 by Marcel duchamp

picon face
Charles Craft wrote:
>>> Anyone done chemical cleaning of boards to remove the oxide before soldering?
>>>
>>> thanks
>>> chuckc
>>>
>> Chemicals to clean pcb's? Try water and kitchen cleanser powder applied
>> with something like Scotch-Brite pads and elbow grease.
>>
>
> I've had good luck with those pads on boards that didn't have solder mask or silk screen.
>
> Have you used it on boards with either/both of those?
>
>

Only once or twice on real old boards that were oxidized.

Properly fabricated boards should not require any special treatment
unless they are older and have oxidized.  If you are concerned about
scrubbing off the mask or silk screen, just rub a little softer.

If you have a kit with a pcb that really needs scrubbing and it seems to
take off the silk screen, take a digital photo first so you will have a
record of the original board to help you placing components.

Good luck!

2007\02\19@122752 by David VanHorn

picon face
>
>
> If you have a kit with a pcb that really needs scrubbing and it seems to
> take off the silk screen, take a digital photo first so you will have a
> record of the original board to help you placing components.


I would just tin the pads again, and then wick them flat before soldering
the SMD parts.

2007\02\19@124058 by Peter Todd

picon face
On Mon, Feb 19, 2007 at 09:04:09AM -0800, Marcel duchamp wrote:
If you have a kit with a pcb that really needs scrubbing and it seems to
> take off the silk screen, take a digital photo first so you will have a
> record of the original board to help you placing components.


Small suggestion... I'd *highly* recomend using a flatbed scanner for
that instead of a digital camera. Taking scans of flat objects, like
pcbs, works extremely well and gets you far more detail than any camera
ever could. Scanners are also fairly cheap, even junk $50 ones are good
enough for that kind of thing:

http://petertodd.ca/art/16-2-intersector/imgs/pcb-front-full.jpg

That photo was resized down from one about 4x bigger, all on a scanner I
rescued from the garbage... 400dpi goes a *long* way.

--
http://www.petertodd.ca

2007\02\19@132554 by Charles Craft

picon face
Thanks for all the suggestions. :-)

http://www.vellemanusa.com/us/enu/product/view/?id=351133

The green of the PCB is integral to the design so that 's why I wanted to be gentle.
Retinning the pads works (as suggested) but I was trying to follow the advice in
the supposed "solder experts" book on the subject. Doesn't always make it in the field.

And I also use the heck out of my wife's scanner for board documentation.
Really need to get one for my office before I scratch the glass bed on hers.


{Original Message removed}

2007\02\19@134950 by peter green

flavicon
face
> The green of the PCB is integral to the design so that 's why I
> wanted to be gentle.
> Retinning the pads works (as suggested) but I was trying to
> follow the advice in
> the supposed "solder experts" book on the subject. Doesn't always
> make it in the field.
tbh for boards like those velleman sell things are big enough that provided you use rosin cored solder and a nice hot iron there really shouldn't be any need for preparatory measures at all.

its only when you get into surfacemount that theese things really start to matter.


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