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Soldering tiny SMD ICs?

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dmg

Tue Feb 22 2011, 11:59PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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Posts: 627

Ive been having some issues with these very small ICs in SMD package.
To make things worse, this IC has a powerpad on the buttom that needs to be soldered for heat dissapation. (its a boost IC)

I was thinking to use solder powder and a heat source to allow it to melt and adhere (without actual contact of the heat source), as I see soldering this thing with an iron nothing short of a pain in the ass.

Does this idea sound feasable? or does anyone else have any methods for tiny things like this?
Also, other then the solder powder method, how would one go about soldering the buttom heat pad without killing the IC from over temperture?

haxor5354

Wed Feb 23 2011, 12:04AM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

im not sure if an induction heater can be used for this application. it would be awesome if there is a specific frequency that only heats up solder, that would make life much easier if you're scavenging old parts from curcuit boards

dmg

Wed Feb 23 2011, 12:07AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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sadly the more sensative logic within the IC itself will be destroyed before you even begin to heat up the solder with induction heating (as the IC probably uses gold wire bonding and will be induced with damaging currents).

Thats the thing I hate about SMDs... they are very compact and usefull.. but also very easy to kill before you even use them in your circuit. (at least I got another 10 of these chips. so I can mess up a few times)

Martin King

Wed Feb 23 2011, 12:36AM

Registered Member #3040 Joined: Tue Jul 27 2010, 03:15PM
Location: South of London. UK
Posts: 237

That's not small! Solder it onto the board before any other parts, stick some paste on all the pads including the thermal one (If the pads aren't pre-tinned then tin them first with solder and remove the excess with solder wick to leave a flat surface. Otherwise they may oxidise during the soldering process and the solder won't flow) .Place the IC then stick it in a (non-preheated) electric oven (toaster oven is ideal as it heats up quicker) don't worry about temperature profiles, just whack the thermostat up to around 250C (with a toaster over that has just two heat settings then pre-heat on the lower setting for about 10 minutes then switch to the higher setting) and WATCH THE BOARD. Once you see the paste melt and flow then wait about 10 more seconds then turn the oven off and open the door BUT DO NOT DISTURB THE BOARD! when it's cooled remove it, if there are any shorts between pins remove them with solder wick. This IC was done with exactly the same method :-

in this oven

It didn't have a thermal pad but the principles the same.

If you're worried about trying it or these IC's are hard to get hold of/expensive then get some cheap IC's that have the same package type (doesn't matter about whether they have a thermal pad or not) and experiment with them first.

Martin.

dmg

Wed Feb 23 2011, 12:52AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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Those results look great.
Ill try that for sure, thank you very much.

Adam Munich

Wed Feb 23 2011, 12:55AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Make it a DIP!

Patience and a steady hand is the only advice I have to offer.

dmg

Wed Feb 23 2011, 01:11AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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A steady hand? that I have.
Patience to solder it like you did? not so much.
I figure Ill use a PCB and go from there using martin's method.

rp181

Wed Feb 23 2011, 01:34AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

Drag soldering those works pretty well.

Especially for those large quad packages. Don't need solder paste, and its quick and clean. Actually pretty easy (my first SMD was drag soldering a .5mm pitch 64 TQFP).

Any tips for a .4mm pitch connector? His my limit today...

haxor5354

Wed Feb 23 2011, 03:37AM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

you're lucky to have the pins on the IC exposed. how are you suppose to solder ICs that have solder joints under the chip it self?

cjk2

Wed Feb 23 2011, 03:54AM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
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Those are fun! Much easier than the QFN's. I use an Aoyue Int. 852A++ which is a Hakko clone to do hot air reflow. I suggest using lots of no clean flux and a good heat source set to around 350 Celsius. have a look here, the video is for a QFN, but this will apply to you as well because you have a thermal pad.
http://www.youtube.com/watch?v=c_Qt5CtUlqY

Edit:
Some more suggestions: An engineer once told me that he sticks a big (0.1") though plated hole right under the thermal pad on the chip and simply sticks an iron in there and solders the pad to the thermal pad. You can also try using a hot plate or toaster oven to reflow the part. I have not tried this method as I use a hot air tool, but others have had good results with this.

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