SMD Hot Air work, tip size and air velocity - Page 1
Forum section: electronics / repair

author: jlmoon
author_rank: Unknown
timestamp: March 19, 2015, 07:12:52 pm
content: I am doing some .5mm pitch QFP .. 240 pin style builds and can not find a small enough diameter application needle for my T5 paste. I find the supplied tip is about 4 times too large for proper amount of paste distribution. I am wondering what others do in this case? At the present time, stencils are not an option with these builds. When using paste, I am wondering what others use as far as the tip size and air velocity when utilizing hot air, do you find the air pushing the paste around and up under the chip when using too small of a tip (increasing the air velocity). Has anyone tried a hot plate set around 200 degrees F or so creating a heat soak temp to speed up the process?Thank you

author: tautech
author_rank: Super Contributor
timestamp: March 19, 2015, 07:30:39 pm
content: Are you aware there are specialized tips available for flat package IC's?Not had to use a PCB preheater myself, but it is an accepted practice.Some just use a hot air gun(paint stripping gun) from underneath.Or Drag solder.....

author: jlmoon
author_rank: Unknown
timestamp: March 19, 2015, 07:46:43 pm
content: Yes, I have seen the quad pack tools. They look like a viable method of installation. I'm not anyone makes one large enough to accommodate a 240 pin (60 per side) device for my Weller WRS3000, I am going to check that out.Thank you

author: ConKbot
author_rank: Super Contributor
timestamp: March 20, 2015, 12:51:23 pm
content: QuoteIf youre not stenciling paste, dont bother with it. Too many hobbyists get enamored with solder paste (and pick and places, but thats a different rant) and end up trying to use the wrong tool for the job. Too much paste and you end up with solder balls everywhere, waiting to wreak havok. Can someone get good results laying paste down by hand and reflowing by hand? Sure, but its easier ime to tack down a few pins, slather it with flux and drag solder with a good hoof tip.

author: jlmoon
author_rank: Unknown
timestamp: March 20, 2015, 06:49:03 pm
content: Lol Conk, solder balls you're not kidding, did the solder paste thing and it kicked my arse. Wound up using concave tip and drag, did a beautiful job. Now to remove that 240 pin .5mm pitch qfp.Thank you

author: nanofrog
author_rank: Super Contributor
timestamp: March 20, 2015, 11:41:41 pm
content: Quote from: jlmoon on March 19, 2015, 07:46:43 pmIIRC, the HAP200 is meant for 30mm x 30mm packages max.But you'd be able to drag solder with your iron (preferably with a gull wing tip).

author: Psi
author_rank: Super Contributor
timestamp: March 21, 2015, 12:02:42 am
content: Yep, ive tried hand pasting 64/100 pin ICs and reflowing them quite a bit.It's more trouble than its worth.Just put on some magnifying glasses (or use a desk mag lamp thing).Apply a good amount of flux to all the pads (very important). Then place the IC and use a small tip iron with some 0.3mm solder wire to hand solder a pin at a time.Drag soldering is faster but takes more practice (except for DFN chips which drag solder awesomely)If you drag solder QFN's use a really wide tip and do like 4 pins at once, remember to drag away from the pin and not across it.It really isn't slow to hand-solder QFP once you get good at it. The joints are better/shiner too.It solders really fast because a single pin as almost no thermal mass. You basically just go around touching each pin and adding a little solder to the iron tip now and then. Because of all the flux the solder on the iron flows off into the pad as soon as you touch it.Fine pitch QFP and hot air just don't mix unless you use a paste stencil.The unevenness in hand pasting always crates bridges, or as you say, the paste runs under the IC.

author: jlmoon
author_rank: Unknown
timestamp: March 23, 2015, 08:53:03 pm
content: Well over the weekend I perfected both new work and rework with installation of 240 pin .5mm pitch FPGA I.C.'s with my project.Psi, you are very correct Paste is not an option when installing those fine pitch parts such as these. I had more solder balls than a NFL game has footballs.Here are a couple of images just for fun.Thanks for all the suggestions