I've been able to use the smallest tip for my weller and some ultra fine solder to solder these chips but I'm not consistent....I shake too darn much. I'm batting about 50%.
Although I've been an electronics enthusiast for years I know absolutely nothing about any soldering techniques other than my iron and solder.
Are there in fact, hot air tools that I could be using to solder the fine pitch parts? Glue the part, and solder with hot air?
Can you simply use the solder that is already on the "solder plated" traces to "reflow" and make a reliable connection to the chip? Or do you add additional solder?
Do the surface mount chips have tinned leads?
Like I say, I have no experience whatsoever with any of this.
If there is a hot air system I could be using what can anyone recommend as a "starter" system that could do one'sees and two'sees without alot of expense?
At my age I need to use a stereo zoom microscope to see that stuff. I prefer water soluble flux which I liberally apply over the IC pins covering them completely. A small amount of solder is applied at the junction of the pin row and the soldering iron (Metcal) tip. I prefer to push the tip instead of dragging it. If you have enough flux three will be no oxidation of the solder which kills the surface tension. It is the surface tension of molten solder that caused it to snap back instead of forming unsightly rat tail. Did I mention the you have to use plenty of flux? You can do the same with rosin based solder and flux. Water washable flux has to be cleaned immediately else left in air it reacts with humidity and polymerizes into some weird goo that is hard to clean off. If you cannot clean the board soldered using water based flux than store it in airtight container along wit some desiccant.
For onesies and twosies I would not bother with hot air equipment unless you routinely need to remove and reinstall chips on the same lands.
Use a flux pen liberally on the lands before putting down the component. The object is to make the solder wet the land and lead and use surface tension to keep the bead from sagging and shorting to the next pin.
If you leave an individual joint hot for more than a few seconds, you will boil the flux out of it and it will not flow properly. Add more solder and use wick to get the excess off. Rosin-impregnated solder wick is very helpful for this.
HASL leaves enough solder on the surface to tack the chip down at the corners but not to hold it down permanently, you need to add enough solder to form a good fillet.
Depends on the process, particularly with evil RoHS bullshit producing a new generation of problem parts. But you can rely on PbSn solder with rosin core flux being able to wet the leads, which amounts to the same thing.
At my age, I prefer to use 3.5 or 4 diopter reading glasses for 10$ from the supermarket. The advantage over a microscpe is that I can adjust the distance and angle by moving the head.
Tack down the chip by hand-soldering a couple of corner pins. These joints can be mediocre. Make sure alignment is good.
Wet all the pins well with liquid RMA flux.
Clean your tip, add a little blob of fresh solder, and quickly run it down a row of pins. Solder will wick off the tip and solder the pins as you slide down the row. Hit the ugly corner pins as you pass.
They make "hoof" soldering iron tips that are optimized for this, with a little flat area that stores a blob of solder.
What is RMA flux, John? I took a little one day minicourse in SMD assembly where we used a flux that had the appearance and consistency of water. Is that the stuff you are talking about and where do you get it? What do you clean it with?
I've found that a nice hot toddy can calm your nerves a lot. ;-) I haven't done those little bitty packages, but I have unsoldered and soldered SMT resistors and capacitors (back in the days when you could actually see individual components), But everybody seems to say, tin two pads on opposite corners of the pattern. Flux them sparingly (like with a syringe), set the chip down and hold it, then just touch each of the corner leads (over the tinned pads) to sweat-solder them in place, then flux the rest of the pins and just drag a solder ball over them - this is supposed to work; I've never tried it but I can see myself doing it as long as I had the right eyewear (like a 3X magnigier. ;-) )
I have used a Pace soldering iron with a fairly large tip with a hole in it. (I can't remember what its called now) You, tack the IC making sure alignment is perfect, fill the hole up with solder, coat the pins with RMA flux and run the iron down the pins. I have used this technique for a while and find it very fast and easy.
Rosin, Mildly Activated. It's sticky, gooey, solvent-soluble, non-conductive, brown/amber liquid, viscosity and color about like maple syrup. You can dilute it a little with alcohol for the SSOP soldering thing, maybe.
Clean with any nice solvent. We have a vapor degreaser with some exotic 3M stuff in it. Most hand-washing is done with isopropyl alcohol, although I like acetone, nasty and toxic as it is.
RMA flux is great. If you have a cruddy, dull solder joint, apply a tiny dab and touch it with an iron, and it'll instantly get smooth and shiny.
Yeah, I've done evrything you're talking about...sorry but my original question was about "hot air".
Is there actually some sort of hot air system that will solder?
I've done everything you can think of with my iron and yes most of the time I can do fine pitch parts with all the techiniques mentioned.....I'm looking for info on "hot air" and reflow.
Forget hot air. Yes, there are hot air guns and there are reflow boxes built from pizza ovens. But considering the purpose, soldering prototypes, they are compared with just an iron. You'd have to go into paste masks, paste drying up, this sort of hassles.
Bloody SM ICs. I use my normal Weller 50W 3mm chisel bit. Trick is to do the pins en-masse. Freshly tin the PCB pads. Force the IC body in position with something long and pointy. Tack solder the outside corner pins. Wipe tip clean. Run down each side of the IC eith the iron. SM IC pins fuse easily with the freshly fluxed and soldered PCB pads. If I had any, I'd use some liquid flux but I don't, so I don't but as I'm not seeing failures I don't make the effort. john
I think that depends on how many units you have to construct. I have made
100's of prototype's over the past couple of years and I usually do it with a dispenser, some solder paste (to avoid paste mask), tweezers and a mini oven where I can easily control the temp. Its a great way to do it if you have more than a couple of boards to build. I usually load resistors and other passive components like this but use the "Tip with a hole" for and IC smaller than an SOIC. I have found that using paste on SSOP packages always ends up with bridges or dry joints and usually require a touch up with some flux and an iron anyway. The paste/heat technique works well for me and I once constructed 10 x PCB's with 250 parts each in about 14 hours including the pasting........ It was a very long 14 hours.
This was generally adopted for mass production use by a company here in Cambridge after trying e.g. the Weller desoldering station with its massive nitrogen bottles etc.
It is a trifle nerve wracking to begin with e.g. you can blow away the surrounding surface components of the thing being desoldered if you use high air speed and don't blow vertically down.
But with practice it is *fast* and *safe* e.g. using heat setting 6 and low airspeed, we were able to desolder the *plastic" battery contacts on an eight layer board without melting them, and then put them back again.
We routinely removed/replaced large quad packages:-
1) Set to 7, use the half inch nozzle.
2) Hold vertically above.
3) Patiently direct the heat with slight circulating motion if the package is large.
4) Notice the smell as the flux begins to melt, say after 30 seconds to
60 seconds. Sometimes this can take 2 minutes. If it takes say 15 seconds, the heat is too much!
5) Gently prod the package laterally to see if it is free. (Don't pull upwards! - (yet))
6) Using same tweezers:- (Safer-grab, risk-of-drop) grip opposite sides of package and lift cleanly upwards (more-dangerous-grab less-risk-of-drop) grip top and bottom of package after sliding one prong of tweezer under and lift cleanly upwards.
7) DO NOT DROP see 10).
8) And then immediately clean the pads with the solder braid and weller large tip no7 iron you have ready heated to hand.
9) (Easy but slow, (board can cool down)) At your leisure, and using eye-glass, tack opposite corners of new package and use the drag-flow method to resolder each side, wicking off the last two or three pins if necessary.
9) (Fast: mass-production-bored-experts) Immediately flux the pads and replace the new package using slight sideways taps to nudge it into alignment. You skip 8) using this method and maybe slightly higher heat setting.
The danger here is that at the moment of removal and replacement, all the surrounding components are floating so you much *not* jog the board!
10) When you do jog the board or knock a few out of place... just push them back again with your tweezers. This involves the pat-your-head-while-rubbing-your-tummy-difficulty i.e. you have to keep the hot air vertical, correct height and rotating with one hand while you prod the off-position component with the other.
The same company also settled for the small Weller hot air gun (not nitrogen) for replacing individual e.g. 0805 packages without the danger of knocking everything else out of position.
Yes, but if you only intend to solder virgin ICs and PCBs its easier to tack opposite corners and then use the drag-a-pool-of-solder per-side method provided the pitch is wide enough to discourage wicking.
For very fine pitches you could slap fresh solder over all IC pins and de-wick with solder braid - but this can be frustrating depending on the braid-flux-corrosion-quality: Or you could use the heat gun:-
1) Rapidly coat all virgin pads with fresh solder (i.e. fresh flux) using the drag method with a wide, Weller number 7 tip, to leave neat domes of solder with no inter-pad wicking.
2) Place package on top of domed pads and align correctly.
3) Keeping down-draught vertical, heat the whole (with gun).
If you have too much air-flow, the IC will be blown off-alignment immediately (i.e. no harm done) so repeat 2) and 3).
As the solder melts, the IC will settle down to the correct height. (Some fresh liquid flux is handy here if the process takes too long and burns the flux away). Don't rely on surface tension for final alignment, it might or might not, try to get it right at 2). If it is slightly out of line say 20% it should be OK if the solder is still "fresh" and nicely flowed.
It is possible to nudge it a little for perfection but you don't want to mess about too much because it's a hot job! Better to get 2) right first time and keep your body on the cool side of the heat gun.
NB only use the above mentioned heat-gun, the one with the graduated dial on back-end (was it ten heat settings? Or fourteen?) and LED heat indicators on the barrel and, if I remember correctly, the three position switch in the handle (or was it two?). You need a generous air-flow and good control of both heat and flow.
If the bastard won't align at 2) re-do the domes with less solder, use more speed and less solder. Very little is required, it only takes a second or two for near-perfect regularity.
Evidently if you bend a leg getting it out of the packaging then it won't sit flat so check this first.
Yes, this was *the* tool that everyone used, in SMA and Production by the fault-finders and repair.
The highly expensive desoldering stations were hardly used because they only work properly when perfectly maintained and everything is always done in a rush so they were either blocked and/or oxided or not switched on (it takes time to warm up) and if they were accidently left switched on then they oxidised or someone would get impatient and use the tip as a crow-bar and knock the plating off it.
The heat guns were instantly hot, and vandal proof as well as vandal-hostile to some extent.
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