Replacing SMD elecrolytics

[Brian Roth]

I have various Neve Capricorn A/D, D/A and mic pre cards which have failing lytics (certain values and date codes...not All of the lytics are bad).

I did some Google searching and found a few videos with "suggestions" on how to remove the @%&*$ caps.  The "suggestions" seem like caveman tactics....grab the lytic with needle nose pliers, and rock it back and forth, apparently until:

1.  The PCB solder to lytic "pins" connection fatigues and breaks.

2.  The lytic's "pins" fatigue and break.
.
3,  PCB foil fails (aaargh).


When I "mangle off" the lytic, I delicately solder a Quality radial cap (with carefully formed legs) onto whatever I have to work with on the PCB.

CAVEMAN!!!  <G>  There has to be a better way.

In case anyone is interested, I found this listing at Mouser, which shows the same style of cap (NOT that I intend to use that particular cap):

http://www.mouser.com/ProductDetail/Cornell-Dubilier/AVE107M06D16T-F/?qs=sGAEpiMZZMtZ1n0r9vR22ZHbAXPxCSuoorwbn%252bHFYyE%3d

You can click on "enlarge" to see the bastard and its soldering "pins".

Here is a snap of a cluster of the caps on the actual Capricorn PCB:

 

[JohnRoberts]

Hot air station...

JR

 

[Brian Roth]

Hot air station...

JR

So...with 95% of the capacitor's "leads" hidden beneath the part itself....how do you heat up the "stuff" without melting everything else  in the "neighborhood"???

Obviously I am a Total Dummy.....Olde Through-Hole mindset!  lol  I need a decent video tutorial....


Bri

 

[AusTex64]

Hot air station...

JR

So...with 95% of the capacitor's "leads" hidden beneath the part itself....how do you heat up the "stuff" without melting everything else  in the "neighborhood"???


Obviously I am a Total Dummy.....Olde Through-Hole mindset!  lol  I need a decent video tutorial....


Bri

Use hot air with a metal tube that just fits around the component you wish to remove.  Check out hot air tools, you'll see all kinds of attachments for directing the air exactly where you want it but keeps it off adjacent parts. It does look like those particular rectangular caps might be a beech, but hot air is the only civilized way to deal with it.

 

[Monte McGuire]

You can also get an SMD tweezer soldering handle. You need the tips to have physical contact with either the foil or the SMD pads on the device, but they can work very well. I'm using the Weller WTA 50 now and it's serviceable overall. It's sort of a pain to align and adjust the curved tips (the set screw is just too primitive to be precise), but once aligned, they work pretty well for 2 lead SMD components large and small.

Weller has a newer one that might be nicer, and other companies make them too. If you do SMD with any regularity, you really need a tweezer soldering iron - it's far easier to do simple work and re-work. Hot air can work too, but it's sorta pricey, and I'm not so keen on heating up an entire board. I could be wrong though!

 

[Gareth Connor]

The problem with a hot air desolder tool (and I am talking about Pace and Weller - quality, professional tools) is that there will be air bleed around the nozzle. I don't fancy the chances of survival of the nearby poly caps. Also, the air bleed is likely to reflow the solder on the MELF resistors, the reason being that an electrolytic needs such a quantity of heat to reflow its solder that there will naturally be heating-up of surrounding parts. It will take a month of Sundays to hot-air the electrolytics off the board, and an even longer time to re-work the surrounding parts. A hot air tool is better used when replacing SMD resistors and similar small parts and multi-pin parts such as ICs, for which there are special nozzles for different sizes of IC........ I digress from the cap replacement mission......

Thermal tweezers are a better approach, but building up the skill of getting the exact amount of pressure on both pads simultaneously, and gripping the part to be removed, and gently lifting it off the board at the right time when the solder has melted takes a lot of practice, and I would not want to be practicing on a client's multi-layer PCB! Even with years of experience, there is always the risk of pulling-off a pad.

By far the most efficient method for electrolytic removal is to use two very fine soldering irons, one in each hand. A pair of PACE WJS100 soldering irons (or similar) with 1/16" tips will do a nice job. The two-handed approach gives greater freedom of access to the cap terminals and with a little bit of practice it is possible to reflow the solder and flick the duff cap off its pads in a couple of seconds. Most importantly is to add a small amount of new solder to each pad prior to cap removal. In the 20+ years since the board was assembled, the old solder will have lost its ability to melt cleanly and whatever small amount of flux there may be remaining on the pads will be way-past its best. Addition of new solder adds both flux to the terminals as well as providing a greater area of thermal contact for the soldering iron tips when it comes to removing the failed cap.

Is there any reason not to replace the duff caps with the same style of SMD cap?

Final thought.....
Check the board for electrolyte leakage. It's easy to spot as it leaves an oily-looking film on the PCB surface around the leaky cap.

 

[shabtek]

I may be full of hot air; no first-hand experience--
saw a video where kapton tape was used to shield adjacent components from da heat

 

[dai h.]

hi,

"chipquik" (a very low melting point (136 deg. F/58 deg.C) solder for SMT rework that stays molten for an extended period after heating) might be worth looking into. (Lots of example videos on youtube.)

editadding link to discussion on another forum) :

http://music-electronics-forum.com/t35353/

 

[JohnRoberts]

When removing the faulty caps, you can actually cut them up or grind them off with a dremel tool to get access to clean the solder pads. You do not need to remove them intact, just avoid trashing the PCB traces. 

You can dab some solder paste or tin the solder pads with some fresh solder before reflowing the new parts onto the board.

There is harder stuff than that to deal with... SMD is better suited to young eyes...

JR

 

[bruno2000]

+1 for hot tweezers.  I use them frequently.
Best,
Bruno2000

 

[sodderboy]

I like tweezers. I have a pluggable iron on an Ayoue 701 double hot air rework station.
I recommend going to a MI repair shop and get some practice boards. I am still a newbie with two pair of reading glasses on so Iike to do a few practice picks before I touch the patient
Mike

 

[Brian Roth]

So what makes/models of hot air and/or tweezer rework tools are recommended?  There are a bazillion choices with a huge range of prices.

And, am I correct in thinking that flux liquid or paste should be dabbed onto the solder which is to be heated for component removal?

Bri

 

[bruno2000]

I have a cheap set of tweezers (like $20?) that I have used to de-solder Grayhill PCB switches.  It came with a bunch of interchangeable "jaws".  Great for getting stuff off IMHO.  Yes, LOTS of paste and solder on the jaws and the work.  Grab it and run!
Best,
Bruno2000

 

[Brian Roth]

I have a cheap set of tweezers (like $20?) that I have used to de-solder Grayhill PCB switches.  It came with a bunch of interchangeable "jaws".  Great for getting stuff off IMHO.  Yes, LOTS of paste and solder on the jaws and the work.  Grab it and run!
Best,
Bruno2000

What brand did you buy?  Thanks!

Bri

 

[Brian Roth]

Well, I  just looked around at one of my "fave vendors' websites " for soldering/desoldering:

http://www.howardelectronics.com/

Looks  like I will have to spend upwards of $10,000 to be able to service SMD circuit boards when including the $1000 for a stereo microscope (my eyeballs are old and crappy).

Shrug....I'll stick with through-hole and tell the other folks they have to do total card-swaps when something else craps out.

"No User Servicable Parts Inside of This Unit!"  lol


Bri

 

[bruno2000]

I have a cheap set of tweezers (like $20?) that I have used to de-solder Grayhill PCB switches.  It came with a bunch of interchangeable "jaws".  Great for getting stuff off IMHO.  Yes, LOTS of paste and solder on the jaws and the work.  Grab it and run!
Best,
Bruno2000

What brand did you buy?  Thanks!

Bri

I'll check this weekend.  BTW, I've had a bit of experience on one of those $15k rework stations.  Very nice, but I had about a 65% success rate.  Resistors, caps, all good.  Connectors, a miserable failure.
Best,
Bruno2000

 

[JohnRoberts]

I bought a cheapo chinese POS and it works but I wouldn't recommend it... unless you are as cheap as I am.

I managed to service SMD for years with a regular iron, but hot air is the right tool for the job, especially for hidden pads on the bottom of chips or components.

JR

 

[Andy Peters]

Looks  like I will have to spend upwards of $10,000 to be able to service SMD circuit boards when including the $1000 for a stereo microscope (my eyeballs are old and crappy).

You don't need to spend a grand on the stereoscope. Look for one at surplus sales or your local university auction.

And there's no reason that a hot-air tool should cost more than $500.

-a

 

[sodderboy]

You gotta figure the quantity needing removal.  If it is above like, 200 or so then you can't afford to cheap out.  Get the $150 Hakko tweezers instead of the $50.  I like the tweezers with screw tips because I can make my own steel tips and screw them down.

But I am not doing hundreds of SMD caps.

I use these Ayoue tweezers plugged into a 701 hot air station.

You do not need a microscope unless you are doing SMD IC's.  Then you cannot afford to blow it so you need quality.  For the seldom work I do I use jewelers magnifiers.  I have an old-school strap-on and also like these.  I like the magnification to follow my gaze.

Just DOO it.  On donor boards first.  practice removal/replacement over and over.

 

[Andy Peters]

Looks  like I will have to spend upwards of $10,000 to be able to service SMD circuit boards when including the $1000 for a stereo microscope (my eyeballs are old and crappy).

Last week, the local craft superstore had this magnifying lamp on sale for $55. It has enough magnification to see and work on 0603 resistors and caps and SOIC-8s, and it has enough working distance between the board and the lamp so your soldering tool has room.