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rfdipper
Joined: 19 Mar 2003
Posts: 15
Location: phil
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 15 May 2003 11:36 Effect of plating to microstrip |
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how can i take into consideration the effect of the plating to microstrip circuits? 
is soldermask advisable?
thanks
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jzo777n
Joined: 10 Sep 2002
Posts: 113
Helped: 2
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| 15 May 2003 11:59 |
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Yes, the extra thickness lowers the characteristic impedance of the trace
See http://www.sigcon.com/Pubs/edn/PassivationandSolderMask.htm
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flatulent
Joined: 19 Jul 2002
Posts: 4856
Helped: 292
Location: Middle Earth
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| 15 May 2003 14:42 soldermask |
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| The soldermask will increase the losses.
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eladg
Joined: 13 Jan 2002
Posts: 205
Helped: 4
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| 15 May 2003 14:58 Re: Effect of plating to microstrip |
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how can i take into consideration the effect of the plating to microstrip circuits?
is soldermask advisable?
thanks
it is not good to do it.
do u know th thiknes of the plating ? ( or the glue)
2 u can compare the diffrent betwen stripline and microstrip
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mr_ghz
Joined: 01 Apr 2002
Posts: 294
Helped: 2
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| 15 May 2003 19:38 |
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Hi all,
by coating your microstrip lines with soldermask you will increase the
dielectric constant. This will change the impedance of your line. You can
take this in account and use smaller traces.
The problem is, that you will have differences between two prints
manufactured by the same manufactuerer, but not in the same lot...
(coating material, coating thickness, ...) Making the traces resistent by
silver or gold is (in my opinion) the better idea.
Bye
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twinsen
Joined: 27 Dec 2001
Posts: 104
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| 16 May 2003 10:45 |
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This has me thinking:
If you dont plate or soldermask it, and the copper trace oxidizes..does that make a difference to the characteristics as well?
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mr_ghz
Joined: 01 Apr 2002
Posts: 294
Helped: 2
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| 16 May 2003 17:24 |
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Hi twinsen,
Yes of course. An oxidated copper-trace has (also for lower frequencies)
another impedance, because you have less free electrons that can carry
energy.
So an oxidated microstrip-line will not have your desired impedance and
can cause a reflection...
Bye
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Mazi3
Joined: 29 May 2002
Posts: 101
Helped: 2
Location: Europe
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| 16 May 2003 23:30 |
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well if you do plating with some chemicals that make silver or gold... there is problem with crystal growth. border betwen them is not ppure ohmic contact, but it can be semiconducting 
If you cower the line with solder mash, there will be lower impedance line, thets mean, the microstrip "effective widerness" will become bigger.
If cooper oxidize, the cover is kind of ceramic. that mean low loss and high dielectric constant. (imagine metals like dielectrics with infinite epsilon). becouse line will still be physicaly the same, the impedance would even become higher(becouse ceramic has "lower epsilon than metal"). the thickness of oxide is very low, the change would be neglible
keep the lines clean, do not leave fingerprints or resins, solder only there where you must (Pb an Sn have higher resistance than cooper!!!!!!!!) the surface. if you must clean the surface use organic solvent, or grind with the grinding paper 1200(gratings) or even some kind of polishing.this is becouse, the length of current must be short as possible(skin effect!!!!!!!!).
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rfdipper
Joined: 19 Mar 2003
Posts: 15
Location: phil
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| 19 May 2003 11:23 |
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so whats the best approach to protect the copper traces but not degrading the circuit perfomance much?
are simulation software accurate enough to predict the effect of plating the copper lines?
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jupitorcuu
Joined: 24 Apr 2003
Posts: 84
Location: chinaBJ
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| 19 May 2003 14:11 |
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It may decrease the Microstrip line's impedence,there is a software to can
calculate this Si6000 from
www.polarinstruments.com,,there is also
some useful article about microstripline
and stripleline.
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