Lead Free Silver Solder Repairs

[daveyk]

I like to say, I have a Hakko iron and solder dedicated to lead free repairs on instruments that are lead free.  So I had this instrument in the shop and repaired its "U46" circuit.  I used lead free.  The instrument worked perfect.  When this "U46" circuit fails, it shows the instrument running from mains when it is really running from batteries.  The customer gets the instrument back and it shows running from main.  Grrrr, luckily they are only a days shipping away.  I get it back yesterday.  This morning I look under the microscope and I swear, there is a tin whisker between pins 1 and 2 of the chip (between the soldered pads)!  Used an exacto and cut away the whisker.  The instrument works fine again and shows running on battery.

The chip is only a 8-TSSOP, so its not like its tiny and really close pins.  It's an easy solder.

I may put red glip between the pins, but that makes a mess for the next repair.

I am shocked at how fast this happened.  Thoughts?  Stop using lead free for repairs?

[PKTKS]

(..)
I am shocked at how fast this happened.  Thoughts?  Stop using lead free for repairs?

LEAD FREE is a crappy material.

I am not all that convinced that LEAD is so.. soo ..sooooo bad that it should
be so dramatically banned from tiny little electronics device.

LEAD is a natural element - very VERY *VERY* stable - and AFAIK is has orders
of magnitude better result than LEAD FREE.

in general terms. in specifics I may recall.. much much less cracks.
FAR BETTER EVEN and UNIFORM DISTRIBUTION.
FAR BETTER  SOLDERING RESULTS.
MUCH BETTER storage and reliability
better prices...

I can understand some hairy heads but the bad results are visible enough
to reconsider that LEAD FREE just can not replace LEADED  solder results.

in the very specific bottom line... 
IT JUST IS NOT WORTHY TO ASSUME THE RISK OF A CUSTOMER  SERVICE FAILURE

take no chances assume all possible bad results from LEAD FREE...
and just GO LEADED.

I've done that quite some time ago.  REPAIRS are LEAD-FREE *FREE*

no chances taken

Paul

[tpowell1830]

I also agree with PTKS, lead in solder is not an environmental disaster, for all of the reasons mentioned. Whereas tin is very well known to grow whiskers, which is a disaster for electronics.

[helius]

He didn't say it was difficult to work with, he said it caused tin whiskers that shorted out the pins.
It doesn't matter what station you use, the problem is with the material.

[rhodges]

I hope this is on topic... I have four rolls of SB5 that I bought at Boeing Surplus two decades ago. I have only used SB5 a few times, where I thought I wanted better strength at the solder joint.

I have recently looked for some good information on SB5. But all I find is rather vague on SB5. Also, I have them on ebay for $15 a roll, but no bites. Is there something wrong with SB5?

I usually use SN63, but I also have some 60/40. I have read that 60/40 might be useful if I want a semi-solid state between solid and liquid.

Thanks for any information and advice on SB5! (And I do have a roll of AG4.)

[helius]

Sn95Sb5 is usually used for plumbing and refrigeration. It has a high liquidus (240°C) and is relatively tough. It may present some electromigration issues in DC circuits.
Please note that solder for plumbing uses acid flux (zinc chloride) and should never be used in electronics. Sometimes the flux is in the wire and sometimes it is applied separately.

[wraper]

This morning I look under the microscope and I swear, there is a tin whisker between pins 1 and 2 of the chip (between the soldered pads)!

99% chance it was crappy soldering, not tin whisker. Something like this may happen if soldering was done at high temperature with lack of/already burned flux. Tin whiskers are so thin that very hard to notice under optical microscope. Not to say that growing in such short time is extremely unlikely.

[PKTKS]

At work I use a cheap FX888D on my least used bench, and it performs okay with SAC305. I can't understand the hatred towards lead free at all.
(..)

Don't  think it is hatred ..  We just can not avoid LEAD FREE. period.

The thing is we have to REPAIR a LEAD FREE FAILED device.

and that number of failed devices caused by crappy LEAD FREE material is
substantial and is increasing...

It just makes no sense repairing a failed LEAD FREE joint  caused just
because  of the intrinsic weakness of the material... with the same
crappy material again.. 

chances of having the very same issue again  are  just  too high.

Your customer will not understand that LEAD FREE rubbish ...

It will most likely blame you.. not LEAD FREE   
Paul

[wraper]

At work I use a cheap FX888D on my least used bench, and it performs okay with SAC305. I can't understand the hatred towards lead free at all.
(..)

Don't  think it is hatred ..  We just can not avoid LEAD FREE. period.

The thing is we have to REPAIR a LEAD FREE FAILED device.

and that number of failed devices caused by crappy LEAD FREE material is
substantial and is increasing...

It just makes no sense repairing a failed LEAD FREE joint  caused just
because  of the intrinsic weakness of the material... with the same
crappy material again.. 

chances of having the very same issue again  are  just  too high.

Your customer will not understand that LEAD FREE rubbish ...

It will most likely blame you.. not LEAD FREE   
Paul

. If you are talking about crappy reflow/reball "repairs", they are not a repair to begin with. Just kicking a dead chip.

[PKTKS]

(..)
If you are talking about crappy reflow/reball "repairs", they are not a repair to begin with. Just kicking a dead chip.

nono... reballs are more complicated.

Small arrays are not that sensitive to UNEVEN (non uniform) balls

but large grid arrays are very sensitive and not only the type of the
solder plays a role when remaking. The size of the balls the profile temp..

Lot of stuff to consider.

I am talking about plain joints (which includes large thermal mass ones)
being faulty because they crack or got too dry and became cold joints...

Reballing large grid arrays - i am pretty sure - is mostly done w/LEADED balls
just because they are less prone to have non uniform issues (UNEVEN BALLS)

but some folks insist using LEAD FREE solder paste even in large arrays..

the mileage will vary a lot with moisture temperature air condition
the machine(s) used...

the bottom line is that - it is SAFER to repair w/LEADED.
Less chances of duplicating the problem ... again

Paul

[Niklas]

Are you using the same solder alloy for the reworks as was used when the PCBA was assembled? Also the alloy used in the lead frame of the IC can increase the risk of growing whiskers.

[Bashstreet]

This morning I look under the microscope and I swear, there is a tin whisker between pins 1 and 2 of the chip (between the soldered pads)!

99% chance it was crappy soldering, not tin whisker. Something like this may happen if soldering was done at high temperature with lack of/already burned flux. Tin whiskers are so thin that very hard to notice under optical microscope. Not to say that growing in such short time is extremely unlikely.

I have to agree. I have never experienced tin whiskers in any of my lead free repairs using quality solder or indeed i have never even seen any.
It appears some people seem to get them all the time and some never there must be a reason what it is i do not know. 

And right tin whiskers should take "long" time to grow (unless your in weightless environment)
I use almost elusively tin free QUALITY solder although some work where temperature is critical or other special cases i do use leaded solder.

Maybe we could start a topic where contributors could add pictures and background stories on whisker issues and maybe find most likely scenarios where using leaded solder might be more sensible or at least identity potential risk scenarios for them.

Cheers.

[additude]

(..)
I am shocked at how fast this happened.  Thoughts?  Stop using lead free for repairs?

LEAD FREE is a crappy material.

I am not all that convinced that LEAD is so.. soo ..sooooo bad that it should
be so dramatically banned from tiny little electronics device.

LEAD is a natural element - very VERY *VERY* stable - and AFAIK is has orders
of magnitude better result than LEAD FREE.

in general terms. in specifics I may recall.. much much less cracks.
FAR BETTER EVEN and UNIFORM DISTRIBUTION.
FAR BETTER  SOLDERING RESULTS.
MUCH BETTER storage and reliability
better prices...

I can understand some hairy heads but the bad results are visible enough
to reconsider that LEAD FREE just can not replace LEADED  solder results.

in the very specific bottom line... 
IT JUST IS NOT WORTHY TO ASSUME THE RISK OF A CUSTOMER  SERVICE FAILURE

take no chances assume all possible bad results from LEAD FREE...
and just GO LEADED.

I've done that quite some time ago.  REPAIRS are LEAD-FREE *FREE*

no chances taken

Paul

As far as I have known, thru my manufacturing career, setting up an industrial size wave solder machine with "Lead Free" has always been a nightmare. It was next to impossible. We washed so many boards in solder it was frustrating and took an exorbitant amount of time....
We finally convinced line management to switch back to leaded 63 and soon thereafter the miracle of production came back to fruition.
I never use "Lead Free".... never have, never will..... I've soldered since I was around 7 or 8.....
There's nothing better than  plain ole' 60 or 63 .... especially on the tiny micro stuff.....