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Old 25th February 2013, 12:03 AM   #11
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I do a lot of SMD stuff, I make stencils from copper or brass shim stock using toner transfer.

I read through Mooly's thread, I thought I'd just add this...

If you need to remove a SMD part with legs, such as a TQFP, and you don't mind sacrificing the part, and it's rare that there is a real need to salvage them, then cut it off the board using a scalpel or craft knife. You cut the pins one-by-one as close as possible to the chip. You can hear a quiet 'click' when the blade goes through, it should be stopped by a tiny ledge on the package. You have to work very precisely and carefully using both hands on the knife as quite a lot of force is required, you have to be careful that the blade doesn't slip or snap and damage either you or the board.

When you've cut all the legs the chip will drop off if the board is inverted. Then you can pick up all the cut legs with a hot soldering iron and clean the pads with a bit of braid.

The whole process can be very quick.
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Old 25th February 2013, 08:22 PM   #12
CECCO is offline CECCO  Italy
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Ok boys, this is the outcome of my first smd soldering test.
I think it will be all-right.
I realized that the big challenge is the correct alignment of the parts in the pads.
The joints are made with a 2mm scalpel tip and regular 0.7mm Sn/Pb alloy.
After the solder is applied, i used a desolder braid to clean from the excess.
The pictures were taken with a cheap usb camera.
It is an integrated class D amplifier with embedded TI ADC converter and a pic18 mcu.


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Last edited by CECCO; 25th February 2013 at 08:30 PM.
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Old 26th February 2013, 06:31 AM   #13
Mooly is offline Mooly  United Kingdom
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Looks pretty good to me Well done.
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Old 26th February 2013, 07:24 AM   #14
marce is offline marce  United Kingdom
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It would pass IPC-610 quality any time, impressive, it also shows that SMD is doable for diy
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Old 26th March 2013, 12:53 PM   #15
xrk971 is offline xrk971  United States
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CC,
Nice job. Looks as good as a commercial board. When you say scalpel tip, is that a scalpe tip modified to be a soldering iron or are you using a chisel tip soldering iron? I am debating which tip to use as I have been using kind of a big 0.035 in chisel lately and it has been tough and not the neatest job.
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Old 26th March 2013, 04:49 PM   #16
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Has anyone used this type of SMD protoboard?
"Grid of 42 mil square pads on 50 mil centers allows SMT components of various sizes and pitches to be mounted."

(I found this one and other types at allelectronics.com)
Attached Images
File Type: jpg Protoboard SMT pads1.Jpg (82.4 KB, 50 views)
File Type: jpg Protoboard SMT pads2.Jpg (42.7 KB, 47 views)
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Old 26th March 2013, 05:30 PM   #17
AndrewT is offline AndrewT  Scotland
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50mil = 0.05"
That seems a big pitch for many smd footprints.

sot223 is 2.3mm pin pitch
sot23 is 1.9mm pin pitch and the third pin (collector/drain) is offset by 0.95mm
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Old 27th March 2013, 03:11 AM   #18
xrk971 is offline xrk971  United States
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50 mils is 1.27 mm - small enough but if pitch is off it won't line up with pins on popular ic's. The concept is nice if they perhaps provide various size pitches. The last one I did was 0.65 mm pitch - tiny.

Last edited by xrk971; 27th March 2013 at 03:14 AM.
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Old 27th March 2013, 07:35 AM   #19
marce is offline marce  United Kingdom
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Most modern SMD devices are hard metric pitch and much smaller than 1.27mm (this is the pitch of SOIC IC's).
0.95mm SOT 23
0.65 and 0.5mm SON SOP DFN QFN QFP TSOP
0.4mm QFN
For SOIC based op amp circuits it will suffice quite well with larger SMD caps and resistors.
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Old 18th August 2013, 10:22 PM   #20
CECCO is offline CECCO  Italy
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Quote:
Originally Posted by xrk971 View Post
CC,
Nice job. Looks as good as a commercial board. When you say scalpel tip, is that a scalpe tip modified to be a soldering iron or are you using a chisel tip soldering iron? I am debating which tip to use as I have been using kind of a big 0.035 in chisel lately and it has been tough and not the neatest job.
Hi xrk971.

Sorry for my late reply, I was busy in the last monthts...
I use a Aoyue 968A+ station with a 2mm scalpel tip:

AOYUE SOLDERING,DESOLDERING,HOT AIR REWORK,INFRARED SOLDERING,REPAIRING SYSTEM

the tip is the pn.T-2LD.

This is the method I use to solder smd's:

1 - Place the part in the correct position with the aid of an USB camera. This is the "pain in the a$$" part
2 - While in place, apply solder with the iron on 2-3 pin toghether, no matter if these are shorted.
3 - Repeat step 2 on pins on the opposite side of the IC in order to avoid further component movement.
4 - apply solder on the remaining pins. Don't waste your time trying to avoid shorts, it will be impossible with fine pitch IC's !!!
5 - Remove the excess of solder with a no-clean braid. I found that a 1.27mm large one is OK.
6 - Wash the PCB with a suitable PCB cleaner.
7 - Inspect the joints with the good-old USB camera previoulsy used.

Easy isn'it?
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