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| TQFP soldering troubles |
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| KL27x:
My algorithm is based on results with SMD PCB's and SMD and thru hole prototyping. I have about 15 tips. 13 of them are bevel tips. Then I have a knife and a pointy BR tip. I use a 2.5mm TFO hoof tip for almost everything. 1mm - 2mm TFO hoof tip for point to point bodge wiring/prototyping. Knife tip is occasionally used for removing passives in a batch rework. When you do production soldering, you don't mess up one board, you mess up dozens by the time you notice. The knife can remove passives without adding extra solder, you just leave the passive on the side of the knife and it slides up when you get the next one, until you have a spatula with 6-12 passives stacked on the knife face. With the bevel you have to get a bead going, and then you have to do something with the bead and the little passive swimming in the bead. I have never used the BR tip other than messing around. It looks cool, though. |
| SiliconWizard:
I often use a chisel tip (thin, but largish) for this and don't do drag soldering - I solder several pins at once (according to the width of the tip), then the next pins, etc. Doesn't take that much more time than drag soldering when you get the hang of it, and it doesn't make hardly any bridge. Also, I use gel flux. More effective here than liquid flux. Sure for the very occasional bridge, you use fine solder wick (don't use a too large one that will tend to suck all solder in) and just for less than a second. |
| Shock:
I mentioned this the other day, if you are soldering efficiently you shouldn't need to buy extra work time by adding excessive flux. In that video I posted John Gammell said to not use wick to fix smd drag soldering bridges. I think it makes sense to add a little flux if required and just use a clean tip to fix it. If it was any worse it's a technique problem and that should be remedied first. |
| KL27x:
The only major problem using "too much" flux is the fumes and the mess when it runs through the holes or the routered edges of the board, making the board stick to w/e is under it. I usually just put the piece of cardboard under the board to soak up a bit of the flux. I have begun to use a brush to get just the right amount when prepping boards for production soldering. But most of the time, too much is mainly theoretical. --- Quote ---Doesn't take that much more time than drag soldering when you get the hang of it, and it doesn't make hardly any bridge. Also, I use gel flux. More effective here than liquid flux. --- End quote --- This works ok. But its ergonomically bad. A knife tip is better at this due to the angles. Aside from the ergos demanding just the right angle, this dumps a lot of heat into the pcb (and if you use an old pre-cartridge iron, this can mean a lot of heat into the handpiece.) This tip is also not as good at sucking out bridges, so it's not as forgiving of user error. I find it actually works a little smoother if you angle the edge of the knife so it's almost flush with the row of pins, but slightly angles so only the tip actually touches the pins. The beauty of the hoof is multiple. 1. The cut face is nearly horizontal and on the bottom; this allows it to suck solder bridges out without working very hard against gravity. But with a bead on there and a bit of tilt, it allows the tip to feed the joint very effectively. It's just the right balance. 2. The curved sharp edge is what rolls against the side of a QFN or the toes of a row of pins. This makes for a small contact area of the edge of a large thermal mass to slide over the pins, contacting just a couple at a time. And the curve allows the solder from the cut-face-bead to flowing around the contact point into the joint. 3. The cut-face/solder-reservoir is an oval. Surface tension of solder makes it want to bead into a sphere. On a knife tip, this means the solder beads wants to draw away from the pointy end. On a chisel... it doesn't matter cuz the entire tip and shaft is tinned, and the bead is just an uncontrollable blob, anyhow. When the solder is on the oval cut-face on the bottom of a bevel, it will reach the entire edge, all the way to the edge. This round surface is also efficient regarding surface area:volume of the tinnable area + bead, so the tin doesn't dry out as fast between joints of while on the stand, or make as much smoke. The major downside of a TFO hoof is feeding solder onto the tip. You want to feed solder on the cut face, so this is a bit of twisting and turning if you use "thru hole" methodology. For SMD work, a 2.5-3mm hoof can solder multiple components without stopping, and I just rig my solderwire to hang at the edge of my FOV, for reloads. When you have a bunch of SMD assembly to do, but not quite enough where you fancy putting together and paying for a PCBA order, remember this. And maybe buy some tips to play around with for the job. The chisel tip has no place in SMD soldering, any more than any tip can be used to solder anything, if you really don't have that much to solder in the first place. ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Another thing: With the hoof tip, I routinely do both rows of a gullwing without flipping the board around. And I will do up to 2 sides of a QFN. The front and the right side. Even with a knife, I can't do that, because the angle has to be so exact. It's hard to find. Forget the perpendicular chisel doing anything like that; you probably have to come in somewhere from the east, and have the row of pins lined up just right with your body. With the large bevel, the right angles are a wide range which is extremely forgiving. In this case, with the DIP doing both rows, it's just a 6-7 degree twist of the iron CCW and I don't even need to move or replant my hand. I use the front right edge of the bevel for the front row of gullwing pins (usually top of the toes, but also can be done on the toes). Then I use the left heel of the bevel for the top row; here you can do either, as well. With the QFN doing the second row is just a 1-2 degree twist of the iron and blam, done. Front right of the bevel for the front row. CCW twist of 1-2 degrees, then top to bottom of the right side of the chip, using the front left part of the bevel. (The bottom cut-face of the hoof is always tilting up on the side that is opposite from the row of pins, in general, when drag soldering. More tilt = more stingy; so if you just loaded up on a big blob solder, you can use a bit more tilt. Less tilt will "squeeze" the solder bead against the board, force-feeding the joint, and you can bridge your gullwing IC's.) |
| SiliconWizard:
--- Quote from: KL27x on March 09, 2020, 02:29:12 am --- --- Quote ---Doesn't take that much more time than drag soldering when you get the hang of it, and it doesn't make hardly any bridge. Also, I use gel flux. More effective here than liquid flux. --- End quote --- This works ok. But its ergonomically bad. A knife tip is better at this due to the angles. Aside from the ergos demanding just the right angle, this dumps a lot of heat into the pcb (and if you use an old pre-cartridge iron, this can mean a lot of heat into the handpiece.) This tip is also not as good at sucking out bridges, so it's not as forgiving of user error. --- End quote --- I guess it all depends on the iron you're using and the way you hold it. I mostly use a JBC T210 for small SMD jobs these days, and can hold it in a way that it's not incomfortable at all to do this. But hey, I admit I only do a few prototypes a year and would likely use other methods if I had to do a lot more. I actually started with this method when I had to solder fine-pitch Hirose connectors years back. I didn't really find any other usable method back then, as dragging a tip too close to the plastic part would quickly melt it. Then I found the method rather convenient, and built a habit of using it for pretty much any fine-pitch soldering jobs for similar pins. As to transfering heat into the PCB - not really. Not the way I do it at least. Now it's all in picking the "right" tip for the job. Not all chisel tips will work well with this method. That's again where I appreciate the available JBC tips. Regarding "hoof" tips - I think they are more commonly called "bevel"? - I have one of them. I don't use it very often, but I'll give it a chance for QFPs and see how that goes. |
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