SMT Soldering

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Anyone ever tried something like this?

 

#1 This forum helps those that help themselves

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#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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I use a hand held hot air gun, like the one in the pic for most of my needs.  The preheater is not needed unless your working with BGA devices, which I try not too.

 

Jim

 

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ki0bk wrote:
The preheater is not needed unless your working with BGA devices, ...
... and "heavy" PCB with a lot of copper (the PCB is the heatsink)

A preheater can ease soldering a heatsink to a PCB though in that case might be simpler to use a heat gun under that portion of the PCB.

 

"Dare to be naïve." - Buckminster Fuller

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+1

Preheat ease a lot even for normal PCB's.

Last Edited: Thu. Feb 9, 2017 - 03:30 PM
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yes pre heating is better but it is hurt when you work with 0402... my nose has been burn some time.... ok I do not see like before..

 

Thierry Pottier

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Hands free hot air could be nice.  Bottom heat also.  However it seems too cheap to me.  Some quality control complaints on Amazon.

 

https://www.amazon.com/Aoyue-Digital-Rework-Station-Pre-heater/dp/B00GSCTSMA

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Heat gun stands :

wire frame bench top stand for Master Appliance heat guns

hands-free and bench top, heat gun stand

Might be able to find heat guns of acceptable quality at the local hardware store.

 


https://www.grainger.com/product/MASTER-APPLIANCE-Heat-Gun-Attachment-33M684

https://www.grainger.com/product/STEINEL-Heat-Gun-Stand-5KNR3

 

"Dare to be naïve." - Buckminster Fuller

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I made do with a hand-held gun and lots of aluminum foil over everything else.

 

This was my first introduction to SMT AVRs, and, to be short, it did not go well.

 

I was using a 32u4 and LUFA for USB connection as a 'master' chip that polled six socketed 2313s running in parallel, and while testing the thing it would program just fine, work for awhile, and then quit.  Just stop working.  And it would not respond to reprogramming via the AVR ISP.

 

I pulled out everything socketed from the system, and still dead.  So I put foil over everything else with a neat little razor-bladed window for the chip in question, turned the board upside down, heated and tapped the board until the chip fell off, and then very carefully installed a new one.

 

The new one programmed fine, worked for a few minutes, then quit.  Dead.  Would not reprogram, or even respond to the programmer.

 

I got some more practice about how to smoke off 44-pin TQFP chips without totally cooking the rest of the board.

 

Third chip worked for a little while, then quit.  Splat, dead.

 

Having tested everything else I finally went to the power supply, and what was supposed to be precisely 5.0V was actually putting out 5.8V, just a hair over the spec.  The chips would work fine for a little while, then silently fail, and when they failed, they were dead meat, and removing them and replacing them was no fun at all.  I have been distinctly unhappy with SMT AVRs ever since.

 

S.

 

Edit - Yeah, I know, it's my fault for having a bad supply.  But I still don't like it.  S.

Last Edited: Fri. Feb 10, 2017 - 04:49 PM
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I use the frypan method. As long as I keep the bottom of the board clear, I can put it back on the frypan, heat it up and pick off the bad part. Otherwise, I'll sometimes take a knife and cut the pins off the side of the late lamented AVR, then clean the pads up with my soldering iron and slobber a new one on with the iron.

The largest known prime number: 282589933-1

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I have the Hot air setup and it's OK.  For TQFP pack I use the "Make a mess and clean it up" Technique which works amazingly well, and was shown to me by a wise Freak.

 

To make a mess and clean it up on TQFP packages simply tack one pin on each side of the device, then melt a bead of solder across ALL the pins of the device.  YES, make a solder short across all the pins.  Nothing huge.

 

Next take solder braid and lay it across the bead and press the tip of your iron to it and soak up the excess.  This takes a little practice to master but it works very well.  After you have done this check under a magnifier for shorts.  You will also notice that if done properly you will have a very nicely soldered pin to pad connection.

 

Like I said, it takes practice, but it works amazingly well.

 

 

But on Topic, The preheater is a nice feature as it will aid in the proper flowing of solder for sound connections.

 

JIm

 

 

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Hi Brian, is this for tinkering at home, or for work?

 

Like Torby, I use the frying pad technique these days.

I've used Jim's method also, but in my hands the frying pad technique works better for me.

 

I lay a bead of solder paste down across the pads for the micro, then drop the micro into place.

The photo shows the paste, partially molten, shorting all the pins on a side.

As it heats up more, surface tension and solder mask help to auto-magically remove most of the shorts.

The solder stays with the pins and pads.

 

Afterwards I add a little liquid flux and use the solder braid Jim mentioned to clean up any remaining shorts.

 

This board has more paste than is needed, but it still works fine.

 

Hope we didn't hi-jack your Thread talking about other techniques.

 

I hate posting this image, that X5 PCB has a "minor" flaw. 

The last two times I "fixed" it, as an add on to another PCB, I still didn't get it right...

 

JC

 

 

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Thanks for  the thoughts.

 

This is for small scale assembly of commercial products using lead-free solder.

 

I've tried the 'drag soldering followed by solder wick' method and find it too hit-and-miss for production work. I've looked at low cost ovens but the opinion seems to be that there are too many problems with things like hot- and cold-spots to make them viable.

 

So, at the moment, I'm looking at alternatives.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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jgmdesign wrote:
To make a mess and clean it up on TQFP packages simply tack one pin on each side of the device, then melt a bead of solder across ALL the pins of the device.  YES, make a solder short across all the pins.  Nothing huge.   Next take solder braid and lay it across the bead and press the tip of your iron to it and soak up the excess.  This takes a little practice to master but it works very well.  After you have done this check under a magnifier for shorts.  You will also notice that if done properly you will have a very nicely soldered pin to pad connection.  

 

To clean up this procedure, get a syringe of flux gel - around $15 usd from digikey. Should last for ages. Take the corner pins then put some flux gel on the pins. Then do the solder drag. The flux gel stops the solder joining between pins. The ic will look like it has been reflowed.

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Kartman wrote:

To clean up this procedure, get a syringe of flux gel - around $15 usd from digikey. Should last for ages. Take the corner pins then put some flux gel on the pins. Then do the solder drag. The flux gel stops the solder joining between pins. The ic will look like it has been reflowed.

Those pesky pins.  I use QFN chips so no solder bridges.  Tack flux makes it easier to get and keep the chip positioned correctly.  I've never used no-lead solder.

 

On those rare occasions that I use chips with pins, I curse the bridges.  I'll try the flux on the pin trick

 

I'm glad you mentioned the flux on the pins thing.  It seems obvious to me that flux does 2 important things.  It cleans the surface, of course, but in addition it makes the solder behave itself.  It seems to cause an increase in surface tension that makes the solder want to curl up in a ball.  The molten solder has 2 urges.  The strongest urge is to coat all the copper that has been cleaned with flux.  The other urge is to form a smooth shape with minimal surface area. 

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steve17 wrote:

Kartman wrote:

To clean up this procedure, get a syringe of flux gel - around $15 usd from digikey. Should last for ages. Take the corner pins then put some flux gel on the pins. Then do the solder drag. The flux gel stops the solder joining between pins. The ic will look like it has been reflowed.

Those pesky pins.  I use QFN chips so no solder bridges.  Tack flux makes it easier to get and keep the chip positioned correctly.  I've never used no-lead solder.

 

On those rare occasions that I use chips with pins, I curse the bridges.  I'll try the flux on the pin trick

 

I'm glad you mentioned the flux on the pins thing.  It seems obvious to me that flux does 2 important things.  It cleans the surface, of course, but in addition it makes the solder behave itself.  It seems to cause an increase in surface tension that makes the solder want to curl up in a ball.  The molten solder has 2 urges.  The strongest urge is to coat all the copper that has been cleaned with flux.  The other urge is to form a smooth shape with minimal surface area. 

 

Hmm. I've never had success with the QFN parts. Next time I try one, I'll: 1. Leave the pads extend a bit from the sides of the chip. 2. Don't put anything under the chip. I have a board I'm laying out now with one.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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Torby wrote:

Hmm. I've never had success with the QFN parts. Next time I try one, I'll: 1. Leave the pads extend a bit from the sides of the chip. 2. Don't put anything under the chip. I have a board I'm laying out now with one.

Frying pan, iron, or hot air?  Solder paste or tin the board by drag soldering?

 

I put marks on the board at the corners of the chip to aid alignment.  This picture shows them on the silk screen layer.  I now put them on the copper layer in case the silk screen is not aligned with the copper.

 

 

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Torby wrote:

Hmm. I've never had success with the QFN parts.

If you have a board you suspect has a badly soldered QFN, there could be an easy fix.  If it's just a bad solder job, drag soldering will probably fix it.  It's very easy.  Even your dog can do it.  wink

 

If the chip is positioned on the board badly, then you'll need hot air or a skillet, or something else to melt all the solder.

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I still haven't perfected my qfn technique. Having extended pads certainly helps but i've needed a pin point solder tip to get heat into the chip pad. Again, flux gell saves the day.

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This post is just about drag soldering and soldering in general. No matter how you did the original soldering of a QFN chip, drag soldering can add solder to the joint if necessary and can remove excess solder, including solder bridges.

 

I use 60/40 rosin core solder. Other solders may not work. Some solders won't stick to the iron, like 63/37 solid core, so I have no use for them.

 

Some still think you should hold the solder in your other hand so the solder melts on the board. That used to be true. In the old days, the only flux I had was the stuff in the solder core. As the flux must coat the surface to be soldered, you needed to hold the wire solder on the board so the flux could do it's job.

 

Today we have separate flux so we can flux the parts to be soldered before hand. Then we can put a blob of solder on the iron. When the molten blob hits the parts to be soldered, the soldering takes place quickly. The speed of the soldering varies with the amount of copper that needs heating. Soldering header pins requires a lot more time than soldering an 0603 chip resistor. The only time your other hand should touch the roll of solder is when putting a blob on the iron. After that, you can put that hand in your pocket to keep it out of trouble. :)

 

People use various soldering iron tips. Some have flat spots like the bevel tip and the chisel tip. I guess they work but I don't like them. The flat spot tells me the exact orientation of the tip on the board will make a difference. Some conical tips have a sharp tip. That tip is worse than useless. It doesn't hold solder and there is not enough heat getting to it to do anything.

 

I prefer a bent conical tip. This gives me a convex surface so the exact orientation is not critical. I think you can buy a bent tip but I bend them myself with needle nose pliers. The tip is soft copper and bends easily. The exact dimensions of the tip are probably not critical. I show pictures of the tip I use. In the right picture you can see the solder blob. When that touches the parts to be soldered, a "solder bridge" forms. That's where the heat transfer and solder transfer takes place.

 

I also am attaching a lousy movie of drag soldering. I cheated. The chip is already soldered to the board, and it looks like it was soldered okay. How I got the chip located on the board correctly is another story for another day.

 

You start by fluxing the pads.  Then you put the tip on the board beyond the row of pads, Then drag it across all the pads and beyond before lifting the iron. This gives an even coating of solder on all the pads. I also created a solder bridge and show how drag soldering eliminates it. Drag soldering can remove excess solder and add solder if there is a deficiency.  I got more flux on the board than necessary.  This time it didn't matter.  I can clean this water washable flux off the board in 5.7 seconds under the faucet with a toothbrush.

 

 

 

 

A quick drag solder .mov file.  It did not win an Academy Award.  I was nominated for best actor in a lousy movie though.

https://onedrive.live.com/?id=B5C7684D65D52E94%21463&cid=B5C7684D65D52E94

 

 

Last Edited: Mon. Feb 20, 2017 - 06:58 PM
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steve17 wrote:
If the chip is positioned on the board badly, then you'll need hot air ...

QFN soldering tips and tricks - Power House - Blogs - TI E2E Community

by 

Nov 26, 2018

...

When the solder is molten on the pads, stop the airflow and drop the IC on the PCB pads (see Figure 1). The IC will self-align to the PCB pads as long as the solder is liquid. Carefully blowing some hot air again will help support the alignment.

Figure 1: ...

...

...

Uniformly heat up the board from the bottom using a ceramic hot plate set at ~150°C (you can safely go up to 200°C for larger PCBs with eight layers or more).

...

Am leery of any PCB to 200C; pre-heat by convection instead of Figure 1's infrared pre-heater may be preferred.

 

"Dare to be naïve." - Buckminster Fuller

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I have a similar form-factor that uses hi-intensity halogen light rather than blowing hot air.  These are available on ebay.  I was rather dubious as to whether the "heat lamp" method would have enough horsepower to be effective. It actually seems to work like a champ.  The biggest advantage I've found, is since there is no blowing air, small components can be reflowed (or removed) without being blown all over the place.  It applies the light(heat) over a BGA-sized area. Sometimes I'll add some thin metal "shades"  if I want to keep the light within a smaller area, but that is rare--I just let the adjacent parts heat up as well.  It has a ceramic plate heater beneath that gets the board "ready" to have an area heated to soldering temperature by the light.   I believe the light is strong enough, on its own, for small parts (though it might give a larger thermal shock that way). 

 

The only drawback, for my unit, is that the temperature control is a bit raggedy & depends on some funky  probe PCB "finger" that never seems to stay in place.  I end up just dialing up/down the temperature until I get the results I want.

 

An example, there are many:

https://www.ebay.com/itm/T-870A-BGA-Rework-Station-IR-Infrared-SMD-Soldering-Station-Desoldering-best/132700364900?hash=item1ee58ee064:g:yTkAAOSwIs5a6b1E:rk:3:pf:0

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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The reflow ovens use quartz-halogen lamps, so it is a proven technique.

 

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Some solders won't stick to the iron, like 63/37 solid core

Huh.  Is that a 63/37 thing, or a solid core thing?

I've always felt like my soldering iron doesn't "pick up" solder as well as I see on videos of drag soldering, and almost all of my solder is the 63/37 stuff (I never realized that there were any disadvantages to the eutectic...)

 

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My iron always seems to have a cold spot right at the tip. I've had good luck putting a tiny bit of solder on the tip, avoiding the cold spot, putting a drop of kester liquid no-clean flux and pressing the melted droplet to the pin.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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Most hand soldering problems I encounter are solved by adding liberal amounts of flux.

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El Tangas wrote:

Most hand soldering problems I encounter are solved by adding liberal amounts of flux.

 

And if that doesn't work, use liberal amounts of hammer...

 

- S

 

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I've never had much luck with hand soldering, even using flux