Solder paste type

Looking to mount some XM-L's on stars but having a hard time finding which solder paste is best for this. I came across Mouser and they seem only to have the flux or the silver type like this one http://www.iso-tip.com/products-page/smart-paste-series/silver-bearing-solder-paste-7459/
any suggestions welcome.

I'll just tap onto this and add, is there one that is considered optimum for thermal transfer (eg. for direct-to-copper) that doesn't break the bank? I've got the cheap DX stuff, which does most jobs fine, but if I'm reflowing onto copper sinkpads I probably should investigate paste that's designed for better thermal transfer?

RoGuE_StreaK said:

I'll just tap onto this and add, is there one that is considered optimum for thermal transfer (eg. for direct-to-copper) that doesn't break the bank? I've got the cheap DX stuff, which does most jobs fine, but if I'm reflowing onto copper sinkpads I probably should investigate paste that's designed for better thermal transfer?

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Most solders today are ROHS compliant and are predominantly tin, so thermal resistance differences are fairly minor between the various formulations.

Semiman

I assume that means lead-free? Any sources of ROHS-compliant paste that doesn't cost an absolute fortune? I just checked my local large electronics supplier, RS Components, and the cheapest lead-free I could find was $81 for 25grams

Getting sidetracked, but is there some threshold for level of manufacturing where below that threshold you don't need ROHS compliance? Pretty sure all of my components are ROHS compliant, it's just the solder that's the, um, sticking point.
eg. if you send one item that you've made to someone in Europe, will it be blocked for not showing ROHS documentation? Or is it only when you send a container of 1000 items? While I'm all for reducing lead, I'd probably have to make 100 boards to use the equivalent of one fishing sinker's worth of lead. And at my current rate, that'd take a few years...

Check out Digikey, they have a much wider selection and at less money. This link should work for you:

http://www.digikey.com.au/scripts/d...k=1&rohs=1&quantity=0&ptm=0&fid=0&pageSize=25


Volume does not matter, but some products are exempt.

Will you get blocked ... unlikely, but there are people better able to assess this than I am.

Semiman

SemiMan said:

Check out Digikey

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Well I found some reasonably-priced stuff ($24 for 35g), but then remembered why I never deal with Digikey (or Mouser for that matter); $35 shipping. Don't know why they bother having a .com.au version of their site when it's all in the US anyway. The search will continue...

Also found elsewhere some tin/bismuth solders cheap, but on reading up it sounds like they can have issues and their low temp (~135C) probably isn't suited to high-power LEDs.

I got some solder paste from fasttech.com SKU # 1261003 for $3.28 shipped, works just fine.

I bought mine from www.zeph.com, don't know about shipping to down under though as I live in the states....

LilKevin715 said:

I got some solder paste from fasttech.com SKU # 1261003 for $3.28 shipped, works just fine.

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That is lead-tin, not ROHS compliant.

Just use silver solder for everything. The extra conductivity can only help, and the extra cost is inconsequential. If you can afford to spend $10-20 on a single LED, then you can afford to spend another $10-20 on silver solder that will last for years.

SemiMan said:

That is lead-tin, not ROHS compliant.

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Info was for videoman who created the thread. If he is located in the USA then solder paste with lead content isn't a problem.

Pay shipping & I'll send you lead'd or RoHS solder paste. But for thermal efficiency, I suggest copper/tin/gold alloy solder, I'll send you some of that as well if you'd like.

FRITZHID said:

Pay shipping & I'll send you lead'd or RoHS solder paste. But for thermal efficiency, I suggest copper/tin/gold alloy solder, I'll send you some of that as well if you'd like.

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I think you mean Tin/Silver/Copper solder which is better than Tin/Lead, but in application, the difference will be extremely minor. The most conductive solder tends to be Tin/Silver, about 50% better than tin/lead with most of the Tin/Silver, Tin/Silver/Copper about 20-30% better.

Tin/Gold solders are only about 15-20% better than tin/lead and really not worth the cost for this application compared to Tin/Silver.



Oh, thought Rogue had started thread ... but since Videoman, yup don't need ROHS, good practice though.

Semiman

fyrstormer said:

Just use silver solder for everything. The extra conductivity can only help, and the extra cost is inconsequential. If you can afford to spend $10-20 on a single LED, then you can afford to spend another $10-20 on silver solder that will last for years.

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You must have some magic paste, paste wont last for years as flux component will dry out. Please note Lead free on copper boards will require a fair bit higher reflow temp to get a good bond

SemiMan said:

I think you mean Tin/Silver/Copper solder which is better than Tin/Lead, but in application, the difference will be extremely minor. The most conductive solder tends to be Tin/Silver, about 50% better than tin/lead with most of the Tin/Silver, Tin/Silver/Copper about 20-30% better.

Tin/Gold solders are only about 15-20% better than tin/lead and really not worth the cost for this application compared to Tin/Silver.



Oh, thought Rogue had started thread ... but since Videoman, yup don't need ROHS, good practice though.

Semiman

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Actually, I ment tin/copper/gold. I have a spool of it here & would happily send him some, along with water soluble OR NO-Clean paste of his choice.
& yes RoHS solders do require higher reflow temps, just make sure everythings clean and dry and you shouldn't have any issues as long as you don't over saturate the heat and cook the pill.
We have special 5 zone reflow ovens for just that purpose, but it can be done on a hot plate, toaster oven, or in gutsy attempts..... A clothes iron.
(I prefer an oven or proper reflow equipment.)

FRITZHID said:

Actually, I ment tin/copper/gold. I have a spool of it here & would happily send him some, along with water soluble OR NO-Clean paste of his choice.
& yes RoHS solders do require higher reflow temps, just make sure everythings clean and dry and you shouldn't have any issues as long as you don't over saturate the heat and cook the pill.
We have special 5 zone reflow ovens for just that purpose, but it can be done on a hot plate, toaster oven, or in gutsy attempts..... A clothes iron.
(I prefer an oven or proper reflow equipment.)

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I have not heard of tin/copper/gold used for regular soldering, sounds more like die attach. Gold is used in solder mainly for mechanical properties and the elimination of flux due to superior wetting. If you want high thermal conductivity, Tin/Silver/Copper is the best and it is not overly expensive. It is harder to solder with as (in addition to temp issues) most copper alloyed solders have poorer wetting.

Semiman

hey guys.. I'm just enjoying the conversation! Never even heard of tin/copper/gold solder before. As a EE, I enjoy these sorts of discussions more than debates over tints.

Is the thermal conductivity of solder significant when applying the average 3W LED? I would have thought that other parts of the thermal path would dominate the thermal resistance. Or is this more for special cases?

i use digikey paste, paid iirc $16 for a surringe full. but the trick is, the paste has to be kept in a fridge, all the time, didgiky recomends 2 day shipping for paste, they mail it in termal bag, with ice bag in it. and you should keep the paste in the fridge, with surringe held in vertical position, before using let it warm up to room temp, for about 8-10 hours.

Steve K said:

Is the thermal conductivity of solder significant when applying the average 3W LED? I would have thought that other parts of the thermal path would dominate the thermal resistance. Or is this more for special cases?

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I think the thinking is that the thermal path has the smallest cross-section at this point in the train.

I don't do any high performance modding or anything, but I just tin the pads with regular solder. When I solder it, I let it flow/self-center, and then push it straight down with an appropriate tool to squeeze out as much solder as I can from between LED and solder pads. This is probably along the same lines of "does it really matter?", but it makes me feel better about it, and it's MY light, so I do what I feel seems best to my ability.

With regards to the refrigeration of solder paste, I imagine it is to keep it from separating out, since you can't very well stir the contents of a syringe if it separates. BUT that is just a guess on my part.

bshanahan14rulz said:

I think the thinking is that the thermal path has the smallest cross-section at this point in the train.

I don't do any high performance modding or anything, but I just tin the pads with regular solder. When I solder it, I let it flow/self-center, and then push it straight down with an appropriate tool to squeeze out as much solder as I can from between LED and solder pads. This is probably along the same lines of "does it really matter?", but it makes me feel better about it, and it's MY light, so I do what I feel seems best to my ability.

With regards to the refrigeration of solder paste, I imagine it is to keep it from separating out, since you can't very well stir the contents of a syringe if it separates. BUT that is just a guess on my part.

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You are mostly correct, the paste is kept cold to preserve the flux however, I've used 3 yr old paste that was kept sealed with no issues, but moisture is the biggest issue with paste solders.
I use RoHS pure tin paste & tin/copper/gold water soluble wire for all my work. Its high conductivity, thermal, strength & corrosion resistances can't be beat. Not ti mention, with the gold alloy, tin whiskering is lesser of an issue,.... But to each their own.