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Through hole capacitors

Discussion in 'Electronic Design' started by colin, Jan 28, 2006.

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  1. colin

    colin Guest

    Hi,
    I had been trying to decouple the power supply of a prototype circuit with
    200mhz+ fast pulses and precision timers, with a smd capacitor on a double
    sided pcb, but found there was still measurable noise on the gnd side of the
    capacitor due to stray inductance. the back side of the pcb is undisturbed
    ground plane with smaler gnd planes on the top side conected with vias. I
    didnt realy have room to route a better gnd conection for another capacitor
    and rather than put the capacitor on the back and disturb the gnd plane I
    had an inspiration and drilled a 1 mm hole and found a 10nf smd capacitor
    fitted through the hole perfectly, the end caps were flush on either side of
    the pcb and cld be soldered ok and the chips power pin put on top of the
    buried capacitor, therefore taking up very little space.

    I had one go short circuit some time later (and it took a while to find as I
    had forgoten it was even there!) but then I find smd components can get
    upset quite quickly when reworking a prototype many times, the capacitor
    cheked out ok when I removed it, although it seemed low in value but
    increased when pressure applied, i find other capacitors can also fail
    simlarlarly varying capacitance with a smal flex of the pcb after being re
    soldered a few times.

    A small array of through hole capacitors at various points solved the noise
    problem.
    I remember old tv tuners used to have square block ceramic wich went through
    a slot in the pcb,
    I was wondering if this is still considered ...

    Colin =^.^=
     
  2. Fred Bloggs

    Fred Bloggs Guest

    I had been trying to decouple the power supply of a prototype circuit with
    They are actually working on integrating the capacitor right into the
    PCB dielectric during board manufacture.
     
  3. Pooh Bear

    Pooh Bear Guest

    Just the one ! ?

    That's your problem !

    Graham
     
  4. Leon

    Leon Guest

    The Pulsonix PCB software I use has that feature (Embedded Component
    Technology). Rs, Cs and inductors may be placed on the inner layers.
    I've never used it, though. :cool:

    Leon
     
  5. Leon

    Leon Guest

    I've heard of that technique being used on PCBs working at microwave
    frequencies.

    Leon
     
  6. colin

    colin Guest

    Interesting, yes I supose the next logical step would be to have ceramic
    instead of fr4 for one of the layers beteewn the power planes :)

    The manafacturing guys would probably have kittens if they had to put
    capacitors inbetween layers, and what about reparing them ?

    I was wondering if there are any big difference in stresses puting them
    through a hole like this.

    we already have pcb printable resistors maybe printable capacitors are next
    ?

    Colin =^.^=
     
  7. colin

    colin Guest

    Well I already had one or two but that wasnt enough so was trying to put one
    more in but kinda ran out of room, adding a leaded capacitor directly accros
    the supply rails didnt cut it either, eventualy had 2x 10nf 1x .1uf and 1x
    1uf in one spot as close as possible (all but the 1uf buried), this cleaned
    up the supply rail nicely for the 100ns 1-3v ramp generator and comparator
    (right next to a 74vhc flip flop but with seperatly fed supplies)

    I made a square wedge wich makes the 1mm hole have corners to acept the 0603
    size wich is 1.1mm corner to corner, maybe they should make round capacitors
    just for this ? althought ive come acros round resistors and diodes,
    soldering is a little bit tricky.

    Colin =^.^=
     
  8. Ken Smith

    Ken Smith Guest

    You can already get high K PCB material so to some degree the capacitors
    have already been made into the material.

    The some years back, Russians made circuit boards with some of the
    discrete parts internal to the PCB. It was done very like blind vias are
    done but capacitors and resistors were placed part way through the
    process. The result was a PCB with chips on both sides and many of the
    other parts hidden inside.
     
  9. Ken Smith skrev:
    Have anyone tried this in practice? And is this technique viable for
    cost sensitive products? And lastly any PCB production companies
    offering this?

    Thanks

    Klaus
     
  10. Ken Smith

    Ken Smith Guest

    Well the russians space folks did do they count? They were trying to sell
    the technology to others.
    NASA thought it was too costly.
     
  11. Joseph2k

    Joseph2k Guest

    Sounds more like something the NSA would do.
     
  12. Ken Smith

    Ken Smith Guest

    Some NASA payloads are NSA payloads.
     
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