Solder Joints

[killian6pk]

What makes solder joints go cold?
I have been working on a Dell E207 WFPc and since Inverter Transformer Joints seem to give so much trouble I decided to reflow them. On 3 of the joints just as soon as they cooled they went cold joint on me. So I removed all the solder from all of the pins and resoldered them. The same 3 pins went cold again. I think I am getting the joints hot enough on the pad and the pin. Any ideas.

[PlainBill]

Re: Solder Joints

What makes solder joints go cold?
I have been working on a Dell E207 WFPc and since Inverter Transformer Joints seem to give so much trouble I decided to reflow them. On 3 of the joints just as soon as they cooled they went cold joint on me. So I removed all the solder from all of the pins and resoldered them. The same 3 pins went cold again. I think I am getting the joints hot enough on the pad and the pin. Any ideas.

The usual cause is the board or the pin was not heated hot enough and the solder cooled too quickly. Any movement as it is cooling will cause problems. Lead free solder is also a factor.

PlainBill

[retiredcaps]

Re: Solder Joints

What makes solder joints go cold?

I like this youtube video on how to solder. It talks about technique and cold solder joints.

http://www.youtube.com/watch?v=I_NU2ruzyc4

[PCBONEZ]

Re: Solder Joints

Another thought is that lead-free solder looks kind of dull compared to leaded.
.

[killian6pk]

Re: Solder Joints

Thanks guys. I am using 63/37 solder and basically I'm doing everything talked about in the referenced video. If it was all the joints I would be inclined to believe it was my technique. Since it is only 3 joints out of 6 or 7 it made me wonder if there was something else wrong.

Thanks to whoever put the little beer Smillie in the group to the right. I have been trying to figure out how to accomplish that.

[Krankshaft]

Re: Solder Joints

Too low of a wattage soldering iron can cause bad joints. Joints with high thermal capacity (larger traces like ground planes for example) will act as a huge heatsink cooling the tip of the iron.

This will prevent the pad from reaching the proper temperature to get a good joint but can be enough to melt the solder.

[popeye]

Re: Solder Joints

What makes solder joints go cold?
I have been working on a Dell E207 WFPc and since Inverter Transformer Joints seem to give so much trouble I decided to reflow them. On 3 of the joints just as soon as they cooled they went cold joint on me. So I removed all the solder from all of the pins and resoldered them. The same 3 pins went cold again. I think I am getting the joints hot enough on the pad and the pin. Any ideas.

Any chance of a picture and what type of tip and what tempr is your iron at.

[killian6pk]

Re: Solder Joints

Yes, I will have to post it tomorrow. The tip is a chisel a little smaller than the pads. The temp. is 700 deg. Have not had this trouble before. Usually if it happens it is when I am adding solder. If it happens I can usually suck up the solder and put new down and that takes care of the problem, but like I said it did not help this time.

[mariushm]

Re: Solder Joints

700 degrees? That's 370c ... kind of A LOT. But usually people with temperature controlled stations set them to 300-350c as the tip generally has lower temperature than the rest and when touching what you want to solder it cools down a bit.

The 63/37 is a bit different than the regular 60/40 or the solder free kind, in the sense that it's euctetic, it turns liquid within a very small range of temperature (usually exactly 183C). It also turns solid much faster.
In comparison the 60/40 stays liquid at around 188c/370f and the lead free kinds at ~ 217c.. See http://en.wikipedia.org/wiki/Solder#Lead_solder

Maybe you're just lifting the gun when the solder is already turning solid, therefore disturbing it?

[severach]

Re: Solder Joints

Lack of flux makes a joint cold because the soldering never happens. Flux is required for clean and shiny joints and the flux in the solder may not be at the right place at the right time.

[Krankshaft]

Re: Solder Joints

If you're using a good multicore rosin flux like Kester and not some no name Chinese crap flux shouldn't be the issue and it should be right where you need it.

I keep the temperature of my iron at 350C that's 662F.

Do you routinely clean your tip with a brass shaving cleaner, wet sponge, or a tip tinner? Oxidation on the tip from burning flux will erode the iron plating and cause heat transfer issues.

[killian6pk]

Re: Solder Joints

Pictures of Iron. Could not get clear picture of tip. It is a small chisel tip. Sorry picture must have been too big I will try to resize it and repost.

[killian6pk]

Re: Solder Joints

Try it again.

[killian6pk]

Re: Solder Joints

I will reduce my temp to 660 -670 and try that. The solder is good. I am using a both a sponge and the brass shavings. The tips that go with this station are pre-tinned tips. However they still oxidize some. I wonder if this board used lead free and I am adding leaded back and that could be the problem. Although it is still only on some pins and not on all that I am having this trouble. I tried cleaning the pad with solder wick after using the solder sucker and that seemed to help some.

[Krankshaft]

Re: Solder Joints

If a joint is cracked wick away the lead free and reflow with leaded you don't want to mix solder types.

If the equipment you're working on was manufactured post ROHS it's probably lead free.

[PlainBill]

Re: Solder Joints

One point that bears mentioning. The leads of many components (capacitors for one) are coated iron. If the coating has failed, you could be trying to solder to iron, which is difficult.

PlainBill

[killian6pk]

Re: Solder Joints

Thanks for all the suggestions. I will try until I get it done.