I have had a run around with the CQ WM50HTd Ceramic filter which is fitted in the Motorola T3. Yaesu and other Ham Radio gear have trouble too with better known manufacturers offering.
See my post Motorola TLKR T3.
To me the Pattern of failure seemed to indicate corrosion. One poster on a forum had 3 out of 4 Radios fail between last use and the next switch on, some have mentioned electromigration others excess current actually causing fusing (like blowing a fuse) at switch on..
I dissected the faulty filter.
Only at one end there is a copper / phosphor bronze pressure plate with windows in it, the silvered plate adjacent has verdigris on it from the copper one.
Hmm, corrosion inside a hermetically sealed box ? Rubbish sealing by a rubbish manufacturer more like, plus maybe contamination in the manufacture.
I was not gentle in my opening of the filter I was expecting a hard plastic box so I crushed it in a small vise. This revealed that they had used a soft thermoplastic. This may well explain the breaking of the hermetic seal. SV8YM see below was more careful with his dis assembly he says the pressure plate "keeps everything pressed together when the filter is in its case" that pressure on a soft thermoplastic box will cause the side to bow thus opening the filter to moist air and removing the pressure required for it to work. There is a common factor in the filters taken apart, verdigris on the copper plate. Additionally I think the seal is breaking at this end.
Soft thermoplastic housings are a real pain. From the humble 4 cell battery holder where the cell sticks in the molding despite the spring pressure behind it and the plastic at the positive end moves away, to my Alinco hand held, the accessory 6 cell battery holder gradually took on a bowed shape due to fat NiMH cells and finally split. Maybe I have the only metal clad cell holder, my way of extending its life.
Idiots in manufacturing is not limited to Electronics, a £600 caravan roof vent has a winder mechanism to raise and lower it. The winder drives cogs which mesh into a Bowden cable type worm, the cable needs to be pressed against the cogs so the manufacturer molds a dome on the inside of the gearbox. The gearbox is soft thermoplastic so in a very short time the side with pressure bows and the cogs slip. With that we have a gap open up on a grand scale 3 to 4mm wide.
What ever happened to the proud designers and engineers, things could still be made cheaply using proper materials.
I found more information on the subject of filter death after my dis assembly, it is interesting to find that SV8YM considers it is electromigration, he has found consistently that the filters show a measurable resistance leak to earth. My one instance measured truly open circuit and all ceramic elements and plates were almost clean except for the odd tiny spot of corrosion on the metal plates. The copper / bronze spring and the adjacent plate are clearly the originating place of corrosion.
In my instance the thick ceramic plates only have a small circular silvered contact area on either side, no chance of corrosion salts shorting across the edge of the plate with those.
There is also a theory about applied voltage causing problems, I have no circuit for the T3 so I don't know if there are DC blocking capacitors. Actually there is no need for an external voltage, we have a dissimilar metal cell with the copper plate and its adjacent one which can generate its own voltage when the radio is off, the T3's spend more time off than on so they decay due to electrocorrosion in storage, ready to be dead when needed for use.
Two simple things would certainly help make more reliable filters, a long spring clip made of a non dissimilar metal across the whole stack.
Or a non dissimilar metal version of the present one and a rigid plastic box with the base heat welded for a reliable seal.
I was surprised when looking for a UK supplier by one of the distributors terms and conditions of supply for ceramic filters. Prospective purchasers had to sign a declaration that they were not for use in any application where reliability was critical. Obviously all is not well in the ceramic filter world. The more you look the more you find out that is so.
Read the interesting story from SV8YM here Withering Filters.