SE/30 Logic Board Recap – Experiences with MLCC vs. Tantalum vs. Polymer?

[colopick]

Hello everyone,

I’m currently working on recapping SE/30 logic boards.
As we know, these were originally fitted with SMD electrolytic capacitors, many of which are now leaking, corroded, or electrically unstable.

My goal is to find a long-term reliable replacement solution that stays as close as possible to the original circuit characteristics while also being conservation-friendly – meaning components that will not leak, dry out, or introduce an increased risk of thermal failure.

Since the choice of replacement capacitor type can affect the behavior of the SE/30, I’m interested in how others approach this.

Possible Replacement Types:

1) MLCC (Multilayer Ceramic, e.g., X7R/X5R)
+ Will not leak and has no traditional end-of-life drying issues
+ Excellent high-frequency characteristics
+ Compact SMD sizes
- Capacitance loss under DC bias (especially in higher µF ranges)
- Very low ESR can alter damping and power rail behavior
- Slight logarithmic aging of capacitance over time

2) Tantalum Capacitors
+ Capacitance remains stable over temperature and time
+ Often closer to the original analog behavior of the circuit
+ No electrolyte to dry out
- Polarized → reverse installation results in failure
- Can fail short / go thermal in fault conditions
- Recommended to use generous voltage derating (often 2× the operating voltage)

3) Conductive Polymer Capacitors (e.g., OS-CON, SP-Cap)
+ Very stable capacitance and ESR over the entire lifetime
+ No leakage / no drying out
+ Safe failure mode (non-flammable)
- Larger than MLCCs
- Higher cost

Discussion Points:
• Do you prefer Tantalum, MLCC, or Polymer — and why?
• Are there long-term (>5 years) experience reports with any of these solutions?
• Have you noticed differences in system behavior?
• If MLCCs are used:
- What voltage derating and package sizes have proven reliable?

I'm very interested in hearing your experiences and observations.

Thanks and best regards!

 

[zigzagjoe]

You aren't going to find MLCC of suitable capacitance given voltage derating without them being unusably huge (and expensive). See this thread for details/mishaps: https://68kmla.org/bb/index.php?threads/recap-lc475-mainboard.47648/

Also consider with Tantulum and MLCC: their footprints are radically different from the original caps and traces may be routed in close proximity to original pads. With cap leakage often having weakened the solder mask shorts are not an uncommon experience.

Realistically for bulk capacitance it's not a particularly picky application. Anything will work (and often even works without) so there's not going to be an observable difference in use between the various types of caps aside from mechanical and safety considerations. Personally, I just use high quality standard electrolytics of moderate ESR as the most accurate replacement. The caps used in these machines were some of the earliest SMD caps and would have been cooked in the reflow process, I'm laying odds that modern SMD caps that were hand-soldered will age better.

 

[obsolete]

I was in the middle of writing a reply, then saw that zzj had just written everything I was going to as well or better than I would've, so +1 to everything above

 

[s_pupp]

On at least one of my boards, I piggy-backed two 47uF MLCC caps to account for the DC bias issue. Having obtained them from Jameco at a really low price, it was very cost effective to do so. For a future project, I had planned to age the MLCC capacitors at 12V DC for 1,000 hours or more prior to installing them, but in the end decided to move on to aluminum polymers for a more stock appearance.

 

[colopick]

Thanks for the explanation.

Based on that, do you (@zigzagjoe) have a specific electrolytic cap you’d recommend? I’m looking for something reliable and
close to the original spec.

Also, you mentioned moderate ESR — what would you consider “moderate” ESR in practical terms?

 

[zigzagjoe]

Thanks for the explanation.

Based on that, do you (@zigzagjoe) have a specific electrolytic cap you’d recommend? I’m looking for something reliable and
close to the original spec.

Also, you mentioned moderate ESR — what would you consider “moderate” ESR in practical terms?

Anything marked as "general purpose" is fine, I look for 5000 hours or greater lifetime and 105 deg C rated temperature.
By preference I usually for go for one of Nichicon, Chemi-Con, Wurth (everybody knows red ones go faster), or Panasonic.

 

[Dave928]

i bought a bunch of tantalum cap kits from Circuit5 (6 macs and 3 consoles waiting to get recapped), but am leaning towards using Polymers, simply to maintain the appearance of the originals.

 

[superjer2000]

i bought a bunch of tantalum cap kits from Circuit5 (6 macs and 3 consoles waiting to get recapped), but am leaning towards using Polymers, simply to maintain the appearance of the originals.

I prefer the polymers. I have used hundreds of the 47uf Nichicon polymer caps and they look close enough to stick you wouldn't know they aren't.

 

[Chopsticks]

they might cost more buy solid polymer caps are generally what i use on everything these days that gets recapped. considering they are the same footprints as electrolytic and don't have the same potential long term issues of leaking or drying out for me it makes sense.

to be fair modern tantalum caps aren't known to fail short in the same high numbers the older ones tend to however its sill a failure point to consider. the other issue it footprints though, both the physical sizes and the fact that tantalum caps have the leads wrap under where as electrolytic have the leads fan outwards. this can cause issues in recapping where either the old caps have leaked and be it that or a result of the cleanup the soldermask is removed. Or also the fact that often solder mask will burn of during soldering on these old PCB's anyways and having a internally facing component lead resting on top of a trace when heat is applied along with solder can often just burn of the solder mask anyways.

lastly never use MLCC in place of a polarized cap. its bad practice and a recipe for disaster long term. there's a reason that some caps are polarized and some are bipolar and in 99% of the cases you should adhere to that.

you will find a lot of conflicting information and opinions all over the internet regarding using different types of capacitors. fortunately we have a lot knowledgeable people here on the forum.

 

[cheesestraws]

The other thing worth mentioning about tantalum capacitors is that tantalum is a conflict mineral often mined by, essentially, slave labour. Depending on your ethical stance, you may wish to take this into account; I used to buy tantalums from respectable companies and recommend this but as time goes on I'm getting increasingly sceptical about their supply chain management.

At this point for both technical and social reasons I'd say that solid polymer is probably the way to go.