Help classify a weird part...

[ivaylo]

Not a great fan of these "tell me what this part is" threads, but this one stumped me (and the thing looks sufficiently interesting to ask here). Came from me harvesting parts from a 90s (?) Japanese VCR. Could swear it's a power transistor or a chip, but when googling for the part identificators on the can didn't turn anything out I cut it open. I see two sections of some sort of microstrip or something, one measures infinity resistance the other 38 Ohms or so (not sure I didn't short this one out while "cleaning it").

Appreciate your insights...

[Alex Eisenhut]

Comb filter?

[edavid]

It's a SAW filter.

[ivaylo]

Thank you!

[T3sl4co1l]

Beautiful!  Never seen one magnified before.

Surprised there's so many lines in the thing, I wonder how sharp it is.

In a VCR, that should be due to the, if I remember the modulation correctly, the luminance is pushed to a frequency band above chroma (which remains more or less normal), and very sharp filters are needed to separate them without crosstalk.

You'll also see TVs advertized with comb filters, for the same purpose: sharp filtering of the video spectrum.

Tim

[Falcon69]

What's a "VCR" ?

J/k

Pretty cool.  I like threads like this when you can see the inner workings of components.

[atferrari]

How do they etch such a fine grid? 

[CM800]

Well, Its a heck of a lot easier then doing it on semiconductors, so for a professional industry, I would imagine it would be fairly easy 

[atferrari]

They're photographically masked and etched similar to what is done with printed circuit boards, but the resolution is more in the range of several microns or less rather than say 10 microns for a PCB application.  Just a straight photographic film mask is sufficient down to a few microns resolution, but to get much better than that then you have to start using more sophisticated masking techniques as the patterns become comparable to the wavelength of light and the imperfections in your optics/mechanics.  UV is often used for exposure so that's quite a bit shorter than 1 micron wavelength.  Same sort of optics that were able to be used from the 1950s - 1970s for semiconductor processing of very low resolution devices like discrete transistors and such.

I think they usually sputter coat the metal film a few microns thick or so onto a piezoelectric substrate (quartz probably, could be something more unusual) and then etch.  You can photo mask the areas not to be etched and then etch the metal or you can photomask the areas not to be metallized and then remove the mask after metallization.

It helps that the sputtered metallization is thin rather than trying to etch a 70 micron thick copper sheet as in  the case of PCBs.

Short and to the point. Gracias.