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Alum Electrolytic Caps

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#37054

Alum Electrolytic Caps | 10 October, 2005

Does anyone have any experience running Aluminum Electrolytic Caps with a SAC305 alloy. The profile for the solder calls out a peak temp of 235-255C and 60-75 seconds above 217C. Most can cap manufacturers are calling out for 230-245c max for no longer than 5 seconds. Are the cap manufacturers being conservative on their temperatures, or do I need to look at other solder alternatives.

Thanks,

Nuez

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Rob

#37058

Alum Electrolytic Caps | 11 October, 2005

Hi Nuez,

We've run a number of different brands of SMT Elco's through a number of leadfree temperature profiles, and consistantly the best performers were Elna & a very similar own brand product (not listing here as it was one from a sister company of ours - hence the joint trials).

From memory they had a PBT of 260 degrees C for 15 seconds, against a PBT of 250C for 5 secs for the control sample from Panasonic. (10uf, 16V, 85C, standard).

It's still outside your preferred window, but probably worth a try. Have you tried looking at other paste manufacturers? (Indium, Koki, Almit etc.)

Good luck,

Rob.

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#37086

Alum Electrolytic Caps | 11 October, 2005

Thanks Rob, WE have found some electrolytics that will handle 250C for a few seconds, but Im worried about the reliability.

Haritt

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KEN

#37089

Alum Electrolytic Caps | 11 October, 2005

Yes, let the nightmare begin.

Most electrolytic caps will not meet the 260 minimum and many will not even make 250. These do not meet IPC J-std-020 standards for lead free soldering.

I had one batch of LF boards go through with a spec. of "not to exceed 255 for 10 seconds". Our peak was 250 for less than 3 seconds and still, every cap failed at ATE test. Electrolyte breakdown.

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Rob

#37094

Alum Electrolytic Caps | 12 October, 2005

We've seen issues with Elco's for years on boards with a lot of copper (higher than normal temperatures.

We found that the 250C caps failed on the "burn in" tests as they has lost a lot of electrolyte in the reflow process. On some brands you could spot the likely failures as the can rose off the base where they degassed.

I may have some of the unused samples left - if you let me know what values, voltages, & other important factors, if we have any that mach I'll pass them on for you to test in your process.

Cheers,

Rob.

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#37150

Alum Electrolytic Caps | 14 October, 2005

Thanks Rob,

I have samples and production quantities that we are running on leaded assemblies now. I guess my next question would be, if you are already building lead-free assemblies, how are you processing the electrolity and tantalum caps? The only options is see with out having to change out the solder, would be to install the smt caps by hand or revert back to through-hole parts.

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Rob

#37170

Alum Electrolytic Caps | 17 October, 2005

Hi Harrit,

We are processing SMT eleco's normally - up to around 8mm in height, the larger sizes can still be avoided and are through hole as the cost of them outweigh the benefit of surface mounting them (although we did get good results on test for them).

Regarding tantalum, all A & B cases have been changed over to ceramic & larger size to elco's, where we haven't been able to we have used Kemet & we get very good results.

However, the move away from tants is mainly down to historical issues in sourcing & not lead-free processing as many of you will remember some of the problems over the years in getting hold of them.

I'm really not a fan of hand soldering SMT caps - the footprint isn't designed for it & if your operators are not careful you can get localised heating issues from using a hot air gun or iron that close. If you are going to hand solder you may as well use a through hole part, which will be much quicker if you are going over the wave later.

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