27 Apr
2015
27 Apr
'15
12:53 p.m.
<snip>
Still...I see a lot of people using SMD tantalum parts
to replace SMD aluminum electrolytics, and after seeing so many of these SMD tantalums
burned to a crisp after they developed internal shorts, I certainly wouldn't use them
for general purpose bypass work. SMD solid polymers which do not exhibit that type of
failure mode are readily available in the same case sizes (round cans) as the original
aluminum electrolytics and are also available in the same case sizes as SMD tantalums. Not
only that, but solid polymers are less expensive than tantalum parts.
</snip>
The trick to replacing the aluminum cans with Tantalums is to over-provision substantially
on voltage. A tantalum will eventually react much more violently to transient spikes than
an aluminum can, as such anomalies slowly degrade the oxide layer in the cap, eventually
leading to thermal runaway.
A popular example are the 47uf 16v SMT cans that are common in Apple gear. People replace
them with 16v tants but they should really be going up to about 25v.
If you leave adequate headroom in the voltage spec, you will typically not suffer this
failure. Still agree that if you wanna be truly safe polymer is the way to go.
Cheers,
- Ian
On Apr 26, 2015, at 23:22, Tothwolf <tothwolf at
concentric.net> wrote:
On Mon, 27 Apr 2015, TeoZ wrote:
You can do capacitor repair easily enough with just a soldering iron. I have reworked
dozens of mac and PC motherboards over the years (and a few video cards).
I suspect real hard SMD work (video chips and southbridges) might be popular down the
road to collectors.
Seconded. I don't own a hot air system (yet) and I do plenty of SMD work, including
0402 stuff and sometimes smaller. The single most important thing to have is liquid flux
such as flux pen. You also really want a wide tip (chisel, knife, or hoof) on the
soldering iron to carry molten solder to the joint. This is totally different from
through-hole work since you are applying flux directly to the joint before applying
solder. With enough flux, the right amount of solder just wicks right into the joint (yes,
really!). Even fine pitch QFPs don't give me any trouble.
The only thing I've yet to touch are BGA packages, and I'm really not looking
forward to the day when I have to...