Is there a consensus, or at least reasoned opinions, about creating a printed wiring board (PWB) pad pattern to accommodate both DIP-8 and SO-8 IC packages?
I'm in the early stages of a project involving some IC opamps, and expect there will be some experimentation with different devices before it's finished. I'd like to lay out a PWB that can receive either an 8-pin DIP part, or an SO-8 part. (Although DIP packages are easier to work with in a hobby or prototype environment, many interesting opamps are only available in SMT versions.)
There seem to be four known solutions to this problem:
1. Don't do it. Create separate versions of the board, one for SMT and the other for thru-hole parts.
2. Lay out the PWB for standard DIP-8 packages, then mount the SMT IC onto some kind of adapter board having pins set to standard DIP spacing. There are several commercial versions of this idea - some placing the adapter board parallel to the main PWB, others mounting it at right angle (vertical); some with provision for power decoupling caps or other passive components; etc.
3. Create a custom pad footprint, containing both a DIP-8 pattern and an SO-8 pattern. One version turns the SO-8 pattern 90 degrees inside the DIP-8 outline, and routes topside traces from the SO-8 lands to the DIP pads. If you work with minimum suggested sizes for the pads and lands, it looks like you can maintain 12 mil trace/12 mil space as you route traces between the pads and lands.
4. Create a custom footprint, but position the SO-8 pattern so it straddles one row of the DIP-8 pads. The interconnecting traces between the two patterns are much easier, but the physical footprint of the part is at least 0.1" wider.
I'd like to hear your experiences, comments, or opinions on each of these approaches.
(The remainder of the project I'm starting will probably use a mixture of SMT and thru-hole components. Though I haven't used them for a couple of years, I have several professional and semi-pro PWB layout programs. Apart from the tediousness, I'm not afraid to create custom padstacks for components.)
Dale
I'm in the early stages of a project involving some IC opamps, and expect there will be some experimentation with different devices before it's finished. I'd like to lay out a PWB that can receive either an 8-pin DIP part, or an SO-8 part. (Although DIP packages are easier to work with in a hobby or prototype environment, many interesting opamps are only available in SMT versions.)
There seem to be four known solutions to this problem:
1. Don't do it. Create separate versions of the board, one for SMT and the other for thru-hole parts.
2. Lay out the PWB for standard DIP-8 packages, then mount the SMT IC onto some kind of adapter board having pins set to standard DIP spacing. There are several commercial versions of this idea - some placing the adapter board parallel to the main PWB, others mounting it at right angle (vertical); some with provision for power decoupling caps or other passive components; etc.
3. Create a custom pad footprint, containing both a DIP-8 pattern and an SO-8 pattern. One version turns the SO-8 pattern 90 degrees inside the DIP-8 outline, and routes topside traces from the SO-8 lands to the DIP pads. If you work with minimum suggested sizes for the pads and lands, it looks like you can maintain 12 mil trace/12 mil space as you route traces between the pads and lands.
4. Create a custom footprint, but position the SO-8 pattern so it straddles one row of the DIP-8 pads. The interconnecting traces between the two patterns are much easier, but the physical footprint of the part is at least 0.1" wider.
I'd like to hear your experiences, comments, or opinions on each of these approaches.
(The remainder of the project I'm starting will probably use a mixture of SMT and thru-hole components. Though I haven't used them for a couple of years, I have several professional and semi-pro PWB layout programs. Apart from the tediousness, I'm not afraid to create custom padstacks for components.)
Dale
For 1-offs or protos I try to use only through-hole components (ICs are allways socketed) and later miniaturize once I am happy with the circuit. For the parts (mainly ICs) that are not available in through-hole I build my own little pc boards for smd parts. This way the IC is readily replaced should it fail (I mean if I screw up and let the smoke out). These boards are also available from Futurlec, The Electronic Components and Semiconductor Superstore and way cheaper than Digikey! E
A lot depends on how confident you are with the design.
If it is thought be correct with little doubt then so straight to SMD.
If not then stick to thru hole.
Alternatively put both on the pcb.
If it is thought be correct with little doubt then so straight to SMD.
If not then stick to thru hole.
Alternatively put both on the pcb.
how about just don't bother with DIP op amps any more
you can get most dip op amps in smt so just go smt only
you should use current limited ps to debug so even smt op amps often won't die with good debug start up practices
and (destructive) reworking cheap smt op amps for cirucit debugging where there is a concern about killing the op amp is easy - just shear the legs at the body with an exacto and mop up the leads with solder wick
very low risk of lifting pad with the cut and mop method
you could even plan to put in a sacrifical cheap op amp 1st then replace with the $$ op amp
you can get most dip op amps in smt so just go smt only
you should use current limited ps to debug so even smt op amps often won't die with good debug start up practices
and (destructive) reworking cheap smt op amps for cirucit debugging where there is a concern about killing the op amp is easy - just shear the legs at the body with an exacto and mop up the leads with solder wick
very low risk of lifting pad with the cut and mop method
you could even plan to put in a sacrifical cheap op amp 1st then replace with the $$ op amp
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