Hi all,
I problem I have quite frequently when hand soldering thin film SMD resistors, is that by the time I'm finished, the resistance has increased way out of spec. Is that a matter of using a too hot iron, handling them improperly or something else? How do you do it?
Regards,
Marcel
I problem I have quite frequently when hand soldering thin film SMD resistors, is that by the time I'm finished, the resistance has increased way out of spec. Is that a matter of using a too hot iron, handling them improperly or something else? How do you do it?
Regards,
Marcel
I have not noticed any such problems myself, I primarly use 1% tolerance 0603 size thin film parts and ~350ºC soldering temperature with generous amount of flux. Handling is done with cheap needlenose tweezers and fingers. I can only imagine there possibly being some damage happening to the edges which chips off some material and that ends up causing resistance change...?
Perhaps some manufacturer parts are more sensitive than others, I mostly have Susumu and Yageo made parts in use.
Perhaps some manufacturer parts are more sensitive than others, I mostly have Susumu and Yageo made parts in use.
I first pre-tin the pads and remove the excess solder. Then hold the resistor in the middle with tweezers to the pads,
and quickly tack solder one end just to to hold it in place. Then release the tweezers, and solder the other end.
Then go back and solder the first end.
Place the iron tip on the pad, just touching the end of the resistor. The best iron tip is a short, small chisel shape,
not a long pointed type. I could never get those to work.
https://www.zoro.com/hakko-solderin...AhM0TrAaApN5EALw_wcB&fqc:category=6/4380/8975
and quickly tack solder one end just to to hold it in place. Then release the tweezers, and solder the other end.
Then go back and solder the first end.
Place the iron tip on the pad, just touching the end of the resistor. The best iron tip is a short, small chisel shape,
not a long pointed type. I could never get those to work.
https://www.zoro.com/hakko-solderin...AhM0TrAaApN5EALw_wcB&fqc:category=6/4380/8975
I had the issue with TT Electronics PCF-W0603LF-03-4991-B-P-LT resistors and with TT Electronics PCF-W0603LF-03-1001-B-P-LT resistors, all 0.1 % 0603 types.
In the first case, a 4.99 kohm, 0.1 % resistor had increased to about 12 kohm, but that was after I had desoldered it and mounted it 90 degrees rotated because of a PCB issue. In the second case, I just soldered some 1 kohm resistors to a PCB and found two had increased in value, one to 1.03 kohm and one to 1.07 kohm. I used my finger nail to keep them in place, touched one side with the soldering iron to fix them in place and then soldered both sides.
The soldering iron was hotter than needed, though, namely 450 degrees Celsius, maybe that was simply the issue. I never use long pointed tips.
I used lots of Susumu resistors in another project where I haven't noticed anything going off value, but that could be due to me not measuring enough.
In the first case, a 4.99 kohm, 0.1 % resistor had increased to about 12 kohm, but that was after I had desoldered it and mounted it 90 degrees rotated because of a PCB issue. In the second case, I just soldered some 1 kohm resistors to a PCB and found two had increased in value, one to 1.03 kohm and one to 1.07 kohm. I used my finger nail to keep them in place, touched one side with the soldering iron to fix them in place and then soldered both sides.
The soldering iron was hotter than needed, though, namely 450 degrees Celsius, maybe that was simply the issue. I never use long pointed tips.
I used lots of Susumu resistors in another project where I haven't noticed anything going off value, but that could be due to me not measuring enough.
Yes, the iron temp could be lower, there's little thermal mass to drag it down. Eutectic solder also helps.
Thanks for the replies. I guess next time I'll be a bit more careful with the temperature setting, use a different brand of resistor and hope for the best.
I bought a KSGER soldering system for that reason. The old Weller just had too much heat. I use a setting around 265C to 270C and so far, all good.
Thin films are very thin 🙂 - I can see excess temperature or mechanical scratching being possible routes to damage.
SMT soldering is a question of excess flux, minimal solder, and care never to touch the top of the resistor with the iron,
as this will cause damage to the delicate metal film (which can be of the order of microns thick).
For SMT boards I use a modified sandwich toaster and solder-paste - very good results, reliable. I suggest this or hot-air
as the preferred techniques for handling surface mount - struggling on with a soldering iron is not ideal (been there, never
looked back).
For a doing just a few SMT components I usually do this:
1) apply a blob of solder to one pad.
2) grip the part in ceramic tipped tweezers, apply iron to the blob and place part in place sliding it into position while withdrawing the iron.
3) solder the other end (lots of flux, iron applied to the side/end only)
4) reflow the first side (plenty of flux).
5) clean off the flux
6) close visual inspection with a hand lens.
Its laborious and leaves too much solder, and usually looks ragged.
By comparison doing a whole pcb in one go with an oven/toaster is wonderful, especially using a stencil to apply solder-paste.
BTW ceramic-tipped tweezers are brilliant - no magnetism, happy with heat, tough as anything.
SMT soldering is a question of excess flux, minimal solder, and care never to touch the top of the resistor with the iron,
as this will cause damage to the delicate metal film (which can be of the order of microns thick).
For SMT boards I use a modified sandwich toaster and solder-paste - very good results, reliable. I suggest this or hot-air
as the preferred techniques for handling surface mount - struggling on with a soldering iron is not ideal (been there, never
looked back).
For a doing just a few SMT components I usually do this:
1) apply a blob of solder to one pad.
2) grip the part in ceramic tipped tweezers, apply iron to the blob and place part in place sliding it into position while withdrawing the iron.
3) solder the other end (lots of flux, iron applied to the side/end only)
4) reflow the first side (plenty of flux).
5) clean off the flux
6) close visual inspection with a hand lens.
Its laborious and leaves too much solder, and usually looks ragged.
By comparison doing a whole pcb in one go with an oven/toaster is wonderful, especially using a stencil to apply solder-paste.
BTW ceramic-tipped tweezers are brilliant - no magnetism, happy with heat, tough as anything.
When hand soldering SMD chip components, also take care not to exert much mechanical force on the terminations. These are not meant to handle much other than the thermal stress from cooling from reflow temperature to ambient, a force that will be spread over the entire termination. If you poke at the terminations with an iron, it's possible that the termination could become detached from the resistance film to some degree. That is the only way that I could imagine a 5kΩ resistor could be altered to 12kΩ... near catastrophic failure, and not just overheating the resistance film.
For another project, I've just finished soldering dozens of thin film resistors with many different values, checked all of them, and they were all OK. Most but not all of them were from Susumu. I set the soldering iron to 380 degrees Celsius rather than 450 degrees Celsius.
It guess it was the too hot soldering iron that caused the problem, although it could also be the resistor brand, or maybe I just pressed them too hard before. Besides, most of these new resistors were 0805 rather than 0603. In any case, I'm happy they survived my soldering skills.
It guess it was the too hot soldering iron that caused the problem, although it could also be the resistor brand, or maybe I just pressed them too hard before. Besides, most of these new resistors were 0805 rather than 0603. In any case, I'm happy they survived my soldering skills.
😵😵😵
https://www.susumu.co.jp/usa/tech/rep-data-reflow.php
Product surface temperature
pre-heating 100~ 120 60 ~ 80 sec
Peak temperature 255~ 265 Maximum 5 seconds
·Applicable solder composition:Sn-Ag-Cu solder paste
·Cycles : twice
{Why does the table look great in preview but is all tags on the forum?
I use Susumu thin film 0805. For hand-soldering I route my pcbs with a magnified copper landing pattern than usual which makes soldering much easier. Leaded solder as always and no extra flux besides the intrinsic.
OK, but I haven't a clue what peak temperature the resistor terminal reaches when I set my Weller WSP80 to 380 degrees Celsius. The soldering tip looks like just a piece of metal with no sensors or anything, so I guess the temperature is controlled on the surface of the iron that touches the tip. It depends on the thermal resistance of the tip and thermal capacitance of the tip, PCB trace and resistor what temperature the resistor will reach.
What I do know is that I can't set the temperature much lower or my solder (tin-copper-silver solder with only a slightly higher melting point than tin-lead) won't melt at all. Maybe 340 degrees still works when there are no ground connections (connections to a plane with thermal reliefs).
Then you damaged it mechanically or thermally - SMT components are small and delicate and normally only handled with micro-suction cups.
Possibly reason for the damage. Don't touch the surface, its thin film (ultra thin layer of NiCr commonly, 1000 angstrom or so, ie much thinner than 1 micron)
I use ceramic tweezers and only ever grip the edges, carefully. Never seen such resistance change.
Whoops. Its essential to use a proper temp-controlled iron set correctly with modern components. This much too hot and will easily char the PCB amongst other problems (form oxide layers over metal surfaces preventing wetting by the solder, thermal damage to endcaps or even crack the substrate - which is ceramic).
Endcaps are easily damaged/torn off the actual component when you hold the component not steady: you solder a part to the board and release the tweezer not evenly but push the part slightly sideways. Tiny movements can be enough to cause predamage of the endcaps or tear them off if you´re unlucky/unhandily. And yes, as little heat as possible.
If you want to make your life a hell of a lot easier, don´t use lead-free solder.
Good tweezers, a proper soldering iron (thin tip but still good heat transfer) and ideally use a microsope or at least magnifying glasses.
The latter will magically enable you to hold your hand much more steady and work more precisely.
Magnifying glasses or OK for soldering times <1h with breaks. After that it can get exhausting (eyes + body posture).
If you are soldering SMD regularly I can recommend soldering stations from Metcal and microsopes from Leica
but I´m sure there are more options that are just fine.
A hot plate can come in handy too; with lead-free solder you have to have one. (set somewhere between 40-90°C depending on the job/part/PCB to solder)
Not a problem if you use eutectic lead-free solder, its the non-eutectic stuff that's unworkable. 4% silver is the magic eutectic formula for lead-free.
Anyway if you use solder-paste its a complete non-issue.