CDE has surface-mount acrylic film caps up to 1 uF in 1206. I think Vishay may have some bigger ones. I need an active filter with good settling (low DA caps) and these are candidates. NIC and several others have acrylics to 1 uF.
Any experience with these or similar caps? Any soldering/reliability problems?
We're going to get a bunch of samples and do some DA testing. If they're worse than mylars, I guess we'll use the mylars... they are available up to several uF.
John
FWIW I've had good results with Panasonic ECH series poly caps.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Please note that 'acrylic' parts seem to be descriptive of a single
16V NIC product only. CDE, NIC and other vendors are more likely to source polyester (PE, PET) or polyphenelene sulphide (PPS) as an smd film dielectric. Polycarbonate seems to be a non-starter for smd.I've not heard a dielectric refered to as acrylic, previously, and NIC offers no further info on their website.
RL
John
Acrylate plastics have very low glass-transition temperatures--about 105C for poly(methyl methacrylate) (950k dalton molecular weight).
Much above there, they melt and start to outgas.
Cheers,
Phil Hobbs
Seems you are pitting the melting point of acrylic against that of mylar. I think that there are at least a few variant acrylic formulations, some of which might have a higher MP than mylar. I do not know if there are variant mylar formulations. You may be reduced to buying samples of each type from every possible vendor and testing them at temperature in a fixture using ZERO solder, to find the failure temperature. Then when you find the ONE "decent" vendor of a given capacitor type, you will have to continuously check at least one from every incoming reel or lot.
??? DIY on acrylic?
Of the three, it seems that the first has the best heat resistance (235C for 200 seconds) and the last has ZERO mention...
These caps are rated for 235 or 240C soldering temp.
One of the datasheets refers to "thermoset" acrylic. Another mentions
1500 layers.John
Where did I do that?
Why do I have to do that?
John
Thanks. I appreciate the info.
CDE doesn't currently offer this data sheet in any of their product guides or web links.
From the similarities in the literature, I suspect that there's actually one mfr/source of the part, with Tecate in EU and SA, CDE in NA and NIC in SEA - doing the marketing.
For lead-free processes, I'd stick to PPS.
RL
The PPS caps I've seen are relatively huge. I need to build a 6-pole
50 Hz active lowpass filter, with 7 connector pins, on about a 0.5 square inch pcb. I can get 1 uF acrylic caps in 1206 or 1210, which just barely works. This is a precision situation, so we need low dielectric absorption and good temperature and voltage stability, so ceramics are out.And we like lead!
John
Fine, but the 20% tolerances were not reassuring.
Can you get C0G ceramics that are big enough (yet small enough physically?) I see 0.47uF/50V in 2220.
Where? And how much?
We are leaning towards a mix of PPS for the S-K grounded caps (phenomenally low da, 0.1 uF in 1210) and X7R (OK for the feedback caps, microfarads available in 0805.)
The filter boards will sell for $45 each, so the parts cost does matter.
John
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