Soldering down PLCC PICs

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

Is it regarded good practice to solder down PLCC PIC�s? I was planning to use the TQFP package but they are considerably more expensive that the PLCC package. I�ve only used them in sockets before but this design is on a budget!

Will

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

If the PIC will be installed permanently, then sure. It will make upgrading the software more dificult, unless you are going to do in-circuit programming. The only reason you want to 'socket' the PIC is for upgrades or proto-typing. Soldering is definately more reliable, in my opinion.

Ronald

MikeW · Joined: 15 Sep 2003 Posts: 184 Location: Warrington UK

PLCC is fine if you are having the boards made by a professional company.

I assume that the rest of the components are also smd, so the boards will be manufactured using pick and place machines, and soldered by machines as well.

Hand soldering PLCC packages is not suitable, since the contact between board and pin is underneath the plastic.

I have soldered PLCC for a prototype, but it is hit and miss

Mike

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

PLCC it is then. At over 1UKP cheaper than the TQFP part! But why do Microchip have such a "random" policy of pin numbering, they could at least keep the numbers the same between the 44pin packages!

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

There are some standard packages that have been established but not all of the IC's that are designed have the same count I/O. They simply select the packages that they want to incorporate in their product and then do the best with what has been laid out.

Ronald

jventerprises · Joined: 01 Apr 2004 Posts: 43 Location: Boston

i solder the PLCCs reliably all the time (for customers), BUT i have a 10x optical scope to do it AND a Metcal iron with an appropriate tip. still, it takes some time and is easy to short adjacent pins.

buy the TQFP and save yourself time and annoyance!
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Jon

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

I have hand soldered 44pin PLCC packages for years for US Navy and other marine customers without any problems. I even remove and replace chips. Just keep things clean, hot (750), and fast. I use a common Weller WES50 iron with a fine flat tip. I use a glass for inspection afterward. Soldering using a glass is a pain due to bad depth perception.
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Kasper · Posted: Mon Jun 28, 2004 12:20 pm

Solder braid is your friend for doing fine pitch soldering. I often solder on chips with down to 0.5mm pitch by hand using a regular weller iron. shorts all over, then clean up with solder braid, mop up the left over flux and it looks machine done Smile

for inspecting for shorts, magnification and holding up the board against a light source and you can see even the smallest shorts.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Pace has some short QuickTime videos which show to solder PLCC
packages by a variety of methods. Just click on the links that say Video.
http://www.paceusa.com/_ApplicationSubList.asp?ApplicationGroupID=7#

SteveS · Joined: 27 Oct 2003 Posts: 126

jventerprises · Joined: 01 Apr 2004 Posts: 43 Location: Boston

i agree with the solder braid trick. just solder away and clean it up afterwards with the braid. i do that too. just be careful not to over heat the part. its real easy to do with braid. you can damage some of the smaller parts by applying too much heat.

solder braid does leave a lot of flux residue, so you might want to clean the boards after.....
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Jon

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

The Pace video shows soldering one pin at a time in sucession with an iron. I prefer to solder every other or every third pin first, and come back for the others on later passes. My theory is that it reduces the thermal stress. Like tightening the lug bolts on a wheel it is better to apply the stress evenly than to completely stress one area and then an adjacent area. You can end up with one side of the chip very hot while the others are still cool.

Just my gut feel.
_________________
The search for better is endless. Instead simply find very good and get the job done.