"Frosted" solder joints

[SavannahLion]

The last few times I resoldered or reflowed something on a scrap PCB, it always comes out "frosted". I'm using 60/40 blend. I apply the iron, the solder, it flows, it's nice and shiny when I remove and all is looking good then... BAM! it frosts over in an instant.

All I can think of is that I'm inadvertantly moving the components as it's setting. Yet, even if I don't have my hands on the joints, they're still frosting.

Is there anything else that I'm overlooking? Am I not removing enough of the old solder? Maybe I'm not cleaning the joint well enough? Perhaps I actually need to clamp the components down to prevent movement?

Can any of the soldering guru's enlighten me with their knowledge?

[MonMotha]

Assuming things aren't moving as the joint cools, you're probably not getting enough of the old solder off.  Solder rapidly accumulates impurities that will cause this "frosted" look on the joint.  You may also need a new tip on your iron.

Also, consider using a 63/37 solder.  It will have a slightly higher melting point than 60/40, but it is a "eutectic" alloy, so it won't have a plastic phase during cooling.  Instead, it very rapidly transitions from a full liquid to a solid.  This makes joints less susceptible to movement during cooling.

[RayB]

That used to happen to me all the time when I would over-heat solder. That might be your issue. THe iron is too hot, or you are not yet the master of Touch-Melt-Remove

[Ed_McCarron]

That used to happen to me all the time when I would over-heat solder. That might be your issue. THe iron is too hot, or you are not yet the master of Touch-Melt-Remove

You missed a few steps.

Touch-Melt-Remove-Scream-Blow on fingers-curse

[Frigo]

Try silver bearing solder - I've been using that for all my electronic work and it seems to set really quickly, thus no frosty joints.

[MonMotha]

That used to happen to me all the time when I would over-heat solder. That might be your issue. THe iron is too hot, or you are not yet the master of Touch-Melt-Remove

While you can't really overheat the solder, you can overheat the stuff you're soldering to (components, PCBs, etc.) as well as some fluxes.  This will cause contamination of the solder that forms the joint.  If you're soldering to something gold or silver (silver seems especially bad), this may be what's happening as the solder will attack the gold or silver.  Reducing the time heat is applied will help a lot (try to keep it under 3 seconds), or you can use a silver bearing solder.  For gold plated stuff, just keep the time heat is applied to a minimum as you're not likely to be able to find any solders that won't attack it without buying esoteric stuff online.

Try silver bearing solder - I've been using that for all my electronic work and it seems to set really quickly, thus no frosty joints.

The good silver bearing solder (Sn62Pb36Ag2) is pretty nice stuff, though if can be a little expensive.  If you're going for lead-free, you will need the silver based stuff, of course (the good stuff is close to Sn95.5Ag4Cu0.5).  62/36/2 is a good choice if you have silver plated PCBs or components that have silver plating since it won't eat into the silver in the plating as badly as 60/40 or 63/37.  Most RoHS-compliant components are matte-tin plated, these days, but some passives (mostly high end capacitors) have retained the tin/silver plating of their application surfaces, and one of the most common RoHS-compliant PCB finishes is immersion silver as it's one of the cheapest.

[lilshawn]

it will do that if it was previously lead free solder. the residue on the leads and pads mixes with the new solder and changes it slightly.

electrically it's fine. it's cosmetic only.

[SavannahLion]

Thanks for the info. I was starting to go nuts trying to figure it out.


@MonMotha. How would I know if the tip needs replacing? I did make a mistake and only tinned about half of the tip. The solder refuses to adhere to the upper half now. But that's OK, I don't use that portion nearest the iron (rod?) anyways. Other than that, there are no obvious holes or anything and the tinning is rather shiny most of the time. Even if I only tinned part of the tip, would that cause problems? I don't solder with the non-tinned portion so I don't see how it would interfere. 

The ROHS might be the thing. I doubt there's even a hint of silver in the cheap Chinese made PCB's I'm experimenting with.

[MonMotha]

What kind of soldering iron do you have?

The good tips don't need any special attention when you first receive them as they have a coating on them that will readily accept solder on the entire working area.  High end Weller and Metcal tips should both be like this.  They need replaced when that plating cracks.  You can usually see the crack on close inspection.  Frequent use of solder wick can cause this.  The use of abrasive tip cleaners (those metal shaving stuff) will also wear it down quickly.  I don't recommend those on Weller or Metcal tips.  The "tip tinner" that Radio Shack sells can also destroy these specialized coatings, so I don't recommend it either for these tips.

On Radio Shack and other cheap tips, they need replaced when they're noticeably pitted or when all your solder joints get this frosty look you're talking about.  What happens is that the tip starts getting eaten away by the solder and flux.  This actually happens pretty quickly.  Radio Shack irons are really only suitable for very casual use.  Unfortunately, the cheapie Weller branded irons are also of this style.  If you have a Radio Shack iron and you're getting frosty joints, I'd just go ahead and replace the tip.  They're cheap, and it might fix your problem.  Also consider upgrading your iron.

If you're interested in a reasonably priced, good soldering system, I recommend the Weller WES51.  I use a WESD51, which is just the digital readout/set version of a WES51.  This is a temperature controlled system, and the tips have an Iron/Nickel/Chromium plating that readily accepts solder and does not donate contaminates.  Replacement tips (PES51 compatible) are pretty readily available.  I usually keep an ETP, ETO, and ETS tip around in addition to the stock/included ETA.  The ETA tip is a great general purpose tip, but it's a bit big for 0603 and 0402 passives.

As for RoHS vs. non-RoHS, the non-RoHS stuff is generally considered superior from everything except a pollution POV.  Standard non-RoHS PCB finish is leaded hot-air leveled solder (HAL or HASL).  This is a very good finish and is compatible with both leaded and lead-free solders.  Common RoHS compliant finishes are Nickel/Immersion Gold (ENIG) or Immersion Silver.  Some facilities can offer lead-free HASL, which is probably the best option for hobbyist use, but it's not commonly available.  If you have to go RoHS, pay for the gold finish: it'll keep forever on the shelf (the silver finish tarnishes), and standard leaded/lead-free solders seem to have less of a problem soldering to it than immersion silver.  Just keep the heat on the joint for as little time as possible.  Almost all components you'll buy outside China (and even in, nowadays) are RoHS compliant.  This usually means a matte tin finish, but sometimes a tin/silver finish.  If there's any silver anywhere in the system, it's a good idea to use silver bearing solder.

[SavannahLion]

I'm using an Elenco SL-5 that came with a 9SR6 iron. I think it ran me under $40 for the entire kit. I had a Rat Shack iron as a gift that never got hot enough.

I did read the thread that was put up by erm... I think PBJ that goes into painful detail about the Wellers how they work and model recommendations before I bought the Elenco. At the time, I felt I didn't know enough about soldering to buy such an expensive piece of equipment. You know, I didn't want to shell out a bunch of money on the wrong iron or tin it wrong or whatever. Kind of like buying a 2000 Toyota for your first car instead of a Ferrari Spyder. Make the mistakes with the Toyota and apply the knowledge earned with the Spyder.

[MonMotha]

Iron itself looks so-so.  I'd try replacing the tip.  Should be fairly cheap and may fix your issue.

All this said, as lilshawn pointed out, this is rarely a big problem.  Electrically, it'll work fine, though the frosted appearance is sometimes an indicator that the joint is not mechanically sturdy.

[Frigo]

Just want to jump in on the tip usage, as well. I'm using a 30w fine tip iron from RS, and yeah, I usually replace the tips every 2-3 projects, if not sooner. They're really made for the beginning hobbyist, or someone who has no need for a pro iron. YMMV, but this is what I've gone with so far, and with no real issues that I didn't see coming. To keep it clean, I just use a slightly damp kitchen sponge and wipe the solder off after every 4-5 joint applications. Again, just my 0.02.