Soldering Emitters to Star Boards

[rcnuk]

I'm having soldering problems and hoping for any tips, tricks or suggestions to help me get on track.
Heres my problem:
My order of Seoul Stars from LITEmania came unexpectedly as bare emitters and bare boards. Presenting further practice opportunities for my rudimentary soldering skills. I'm having great difficultly getting the solder to stick on the untinned copper pads of the star. I get a cold joint at best.:thinking: Any ideas? I've tried heat sinking with clips near the pad and extra flux on pad both without luck. The darn pads seem like Teflon to my solder and basically I'm melting the entire top surface of board the to get adhesion in one pad area. After spending a hour destroying emitter and board $s with excesses heating. I took another route and remove the emitter from a Luxeon star. Since the Luxeon board was already tinned it was pretty simple to get a new emitter installed and finish my mod. I guess I could do this for the rest of my starless emitters but hoping that there maybe a way to use the boards that LITEmania sent and keep the Luxeons on there own stars.

My tools for destruction:
I used a cheap 25w RS iron and a HF 30w iron, tinning/cleaning paste, silver solder, 95/5 general solder, rosin flux paste, assorted clips for heat sinking- none with great success on the star boards.

Any comments, tips, tricks or suggestions are welcome!:wave:

 

[FlashCrazy]

Well, aside from these boards having some kind of weird coating, here are some tips:

First of all, you don't want to use the heatsinking clips...they only make it harder for your soldering iron to heat the area. You need to make sure your soldering iron tip is clean, and tin it with solder. The solder should evenly coat the tip with a thin layer of shiny solder. If it doesn't, the tip is either too dirty or just flat worn out. If the tip won't tin well, even after cleaning it with a ScotchBrite pad or fine sandpaper, then replace it.

With a properly tinned tip, place the tip on the copper pad of the star, then quickly touch the strand of solder to the junction between the tip and the star. This will help with heat transfer and the solder should flow onto the pad. In actuality, you should be able to just get a tiny blob of solder on the iron's tip, and just touch the pad of the star...it should flow onto the star's pad.

The other advice is to get some 60/40 rosin core solder...and thin...about .040 diameter or so.

Plus, it wouldn't hurt to clean the stars with some rubbing alcohol.

Hope this helps!

 

[rcnuk]

FlashCrazy,
The tip tinner/cleaner paste does a good job of tinning the tip. I have no problems with melting the solder or getting a nice melted ball on the tip. I just can't get pad area to heat up without excessively heating the entire board. The solder just wants to stay on the tip. When I finally was able to get adhesion the top surface looked like bubblely blackness and the joints look cold. I'll keep practicing since I have theses boards which are currently of no use for modding. I'll also try cleaning the board with alcohol before I start.

One question: I have two types of solder neither I'm guessing are 60/40 like you mentioned. One is silver bearing solder 96 (?)/4 (?) thin rosin core and electrical solder 95 tin/ 5 antimony thicker rosin core. What is the composition of 60/40?

Thanks!

 

[macforsale]

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[will]

Any time I have had problems soldering it is usually that the copper has oxidized. Take some very fine sandpaper, a scotch brite or some thing to clean the area you are going to solder. The flux is supposed to do that, but a little rubbing can't hurt.

 

[matrixshaman]

Yeah it sounds like your problem is likely the solder. Good solder can make all the difference. Silver solder that you mentioned is a lot harder to work with I believe. Sounds like jewelry solder which I think is often done with a tiny butane flame torch. I think what I use is a 5 rosin core tiny size 60/40 and it works great for most electronics. I've even done some of those pepper flake size resistors with it. Unfortunately I can't tell you where I got mine or even what brand it is as I've had it so long the labels are worn off. But it's a high quality that I don't see in places like RatShack unless they have changed their stock lately.

 

[evan9162]

I second cleaning the copper. It's either oxidized, or worse, the construction of the board left varnish on the contacts (not unheard of). The blackening sounds just like what happens when you try to solder to epoxy coated magnet wire - you burn off the epoxy coating, leaving some black sludge in places.

Takes some 300-ish grit sandpaper to the contacts to make sure they're really clean.