Leaking Electrolyte Surface Mount Electrolytic Capacitors SMT

Much aggravation has been caused by surface mount electrolytic caps that develop leaks, leaking the electrolyte onto the circuit boards and creating almost countless faults in a lot of consumer grade electronic gear, and a large number of camcorders.

Spotting electrolytics that develop external leaks isn't too difficult with just a good lighting source, in some cases. In a SONY VCR that I examined recently, when the head amp cover was removed, it was fairly obvious that the SMT caps were leaky.

Around the plastic base of the caps, there were dark speckles under the mask. The mask is a protective coating that's placed on the bare board after the etching is completed, and consists of a very thin layer of translucent sort-of paint, essentially.

When the electrolyte gets on the circuit board, it can creep under the mask, and since it's acidic, it can begin to dissolve the copper traces lying under the mask. This was what had caused the dark speckles that were visible thru the mask, around the bases of the caps in the head amp. For very fine circuit traces, the acid can cause enough deterioration of the traces to cause interrupted paths, or open circuits, but can also in effect turn the copper traces into resistors. Traces under and near the cap bases should be closely examined for deterioration.

To accurately assess the reliability of a circuit board with electrolyte damage, you will need a finely tuned, recently calibrated crystal ball.

The eletrolyte leakage may also be evident on the caps themselves, near the bottoms, below the crimp. The acid can attack the aluminum canister that makes up the covers of the caps, and in the case of the leaky caps in the head amp, the bottom edges of some of the aluminum cans were noticeably discolored from the reaction of the acid on the aluminum.

The acid in the electrolyte can also cause solder to have a dark color with a flat or dull appearance.

In cases where the electrolyte leakage is very limited, leakage can be verified by touching a hot soldering iron tip to the caps leads/solder pads, and detecting a fishy smell.

There are many accounts of symptoms/problems and repairs of equipment with failed, leaky surface mount caps in the archives of SER.

-- Cheers, WB .............

Reply to
Wild_Bill
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Any recommendations for a 7 year old Sony miniDV touch screen Nightshot palmcorder with a failed CCD? Playback is ok. I've given it a good visual and didn't spot anything obvious. A few years before the CCD failed I repaired a bad connection on the LCD display that manifested itself in the form of one missing color.

Reply to
Meat Plow

What datecode range is most suspect? What is the earliest date when this became a widespread problem? Is it yet another example of the counterfeit chinese electrolyte issue?

Michael

Reply to
msg

I haven't been actively involved in consumer electronics servicing for about a decade, so I don't know first hand what the present general failure rate is.

None of this low grade equipment is intended to last long, so there will be more failures. Poor designs, heat and ripple currents of SMPS will ensure that there are short lived appliances and electronic gear in the years to come.

Arm yourself with a good ESR tester like the Bob Parker design if you expect to have a chance of repairing any electronic equipment. Having an analyzer like Sencore's Z-Meters can also be useful for in-circuit checks and evaluation of numerous other components.

No one knows what the reliability will be on their next order of capacitors they receive, even without a huge conspiracy to steal and counterfeit electrolyte formulas, so prepare. With the majority of equipment being built to the lowest price point, manufacturers are likely to buy whatever's on sale this week.

IMO, it's probably best to buy parts like electrolytics from a supplier that buys direct and has a fairly fast inventory turnover, like DigiKey. To have some idea of what you're receiving, test your components when you receive them, and avoid buying large quantities of electrolytics if they'll just sit in a drawer for a year or more.

You might already know that there are date codes on some of the better brands of electrolytics (the usual type with wrappers), so when you see old date codes on new parts, it's time to get a different supplier.

-- Cheers, WB .............

Reply to
Wild_Bill

From my humble experience, mostly camcorders made in the early to mid

90es are affected. I know from Sony Video8-corders from the 80es which still work like a charm but know several from the 90es which are completely failing. I haven't spotted the problem in later models manufactured around 1998/1999. I have still an 1991 Sony CCD-F355E where I want to replace all caps and get it back working just for the sake of repairing it :).

PS: I suggest using an ESR-meter to check the caps which a suspect.

Adrian

Reply to
Adrian Glaubitz

Is it (what leaks from the capacitors) an acid or an alkaline? The difference is important to the method used to neutralize the leakage.

For an Alkaline leakage (batteries and possibly capacitors) you need to use a mild acid such as white vinegar or possibly CLR (not corrosive to copper).

For an acid leakage you need to use a base such as baking powder.

Using the wrong neutralizing agent will only exacerbate the problem!

John :-#)#

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Reply to
John Robertson

From my experience fixing a number of Tek TDS scopes, a good method is a wash of Simple Green cleaner using a brush to scrub the boards, followed by another wash/scrubbing of 99% alcohol.

Reply to
JW

ng

And Macintosh IIci computer boards; many of these from the early nineties had high-fault-rate capacitors.

th

ds,

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The problem is, there's only one solution: replace all those surface mount capacitors. It can take a lot of time, isn't always worth the effort.

Once you see leakage, there's no point in testing (so the ESR is good; so what? you still gotta replace or acid will kill adjacent parts) or cleaning (the reservoir of corrosive goo is still sitting there next to the spill) or even determining which units have failed (there's nine leaks, fourteen capacitors; don't tell me I should just trust the five that didn't leak yet). You have to commit to wholesale component removal and replacement.

I like heat/lift-with-scalpel technique, others may prefer pliers and wick.

Reply to
whit3rd

I expect that you're correct John. Treating/rinsing the location of the base of the leaking capacitor is likely a good practice, but I don't know how effective it would be at reducing the attack taking place under the solder mask, such as what was observed in the head amp circuit of the VCR I just looked at. The 11 leaking caps in an area of about 4 square inches can cause a lot of damage.

I believe the electrolyte leakage I've seen on circuit boards has been acidic, but it's been a long time since I've done any in-depth study of caps. Capacitor electrolyte formulas are said to be closely guarded secrets, but some references are suggested below.

I associate blue-green crystalline material with salt/alkali contact with copper (although I don't know this indication to be a scientific result). Leakage damage from electrolytics that I've seen causes the blackening of metals (solder, copper or tin plating on component leads).

I have some leaky caps presently, but don't have any litmus or pH test strips to test them with.

From freepatents: The operating electrolyte is composed of a quaternary ammonium salt of a carboxyl acid, of an additive of the salt-forming carboxyl acid and of ?-butyrolactone as a solvent. An electrolyte composition for electrolytic capacitors consisting essentially of a salt of a slilcotungstatic or silicomolybdic acid in a polar organic solvent and having a pH of from about 5.0 to about 7.2

From Wikipedia: Electrolytic Capacitor - Electrolyte: The weak acids are usually organic acid (glacial acetic acid, lactic acid, propionic acid, butyric acid, crotonic acid, acrylic acid, phenol, cresol, etc.) or boric acid. The salts employed are often ammonium or metal salts of organic acids (ammonium acetate, ammonium citrate, aluminium acetate, calcium lactate, ammonium oxalate, etc.) or weak inorganic acids (sodium perborate, trisodium phosphate, etc.). Solvent-based electrolytes may be based on organic hydroxyl alkyl amines (monoethanolamine, diethanolamine, triethanolamine,...) or polyols (diethylene glycol, glycerol, etc.).

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Chemistry acid-base relationship Solutions with a pH of seven (7) are said to be neutral, while those with pH values below seven (7) are defined as acidic and those above pH of seven (7) as being basic. A base is also often referred to as an alkali if OH ions are involved.

When utilizing acids for rust removal or other tasks, baking soda is useful for neutralizing those acids.

-- Cheers, WB .............

Reply to
Wild_Bill

There aren't many practical approaches to replacing quantities of leaking surface mount capacitors, other than some type of hot tweezer-type tool.

There are various styles that essentially perform the same function.. to heat both terminals of the device simultaneously, with tips that contact the terminals, or with non-contact hot air nozzles.

That's not to say that it can't be done with basic tools, but servicing electronic gear on a regular basis requires better equipment.

-- Cheers, WB .............

And Macintosh IIci computer boards; many of these from the early nineties had high-fault-rate capacitors.

The problem is, there's only one solution: replace all those surface mount capacitors. It can take a lot of time, isn't always worth the effort.

Once you see leakage, there's no point in testing (so the ESR is good; so what? you still gotta replace or acid will kill adjacent parts) or cleaning (the reservoir of corrosive goo is still sitting there next to the spill) or even determining which units have failed (there's nine leaks, fourteen capacitors; don't tell me I should just trust the five that didn't leak yet). You have to commit to wholesale component removal and replacement.

I like heat/lift-with-scalpel technique, others may prefer pliers and wick.

Reply to
Wild_Bill

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