Surface mount components poorly regarded

[peranders]

Those amps are nice examples of SMT parts.
http://groundsound.com/images/pa3cc_l.jpg
http://groundsound.com
http://mirand.dk/smallheats3.jpg
http://mirand.dk

[BWRX]

Metal film surface mount resistors are certainly fine for all audio applications. Thick film SM resistors are ok too for less critical use and are much cheaper than metal films. If you want precise gain matching go for the 1% or tighter tolerance metal films.

As has been mentioned here and there on this forum, ceramic SM caps with NP0 or C0G dielectric are fine for all audio applications. X7R and other dielectrics aren't as good as NP0/C0G, but work fine for decoupling.

[TwoSpoons]

I love SMT for prototyping because I can avoid all that tedious drilling ...

I have no trouble hand assembling SMT (0603, 0402, QFP etc), even with a fat, butcherous iron. Its all in the technique.

And if you want to parallel resistors, SMTs just stack on top of each other!

All those complaints about Tc etc apply equally to leaded parts - its not specific to SMT .

[head_spaz]

I like the idea of SMT mounted parts, especially the benefit of having a reduced foot print. Soldering can be a challenge, but it is doable.
But my big complaint with SMT is that the resistor and cap ends can easily snap loose if the board gets bent or twisted a little bit.

[peranders]

Originally posted by head_spaz
But my big complaint with SMT is that the resistor and cap ends can easily snap loose if the board gets bent or twisted a little bit.

I have never exeperienced this even with heavy and large boards out there in the industry. How did you manage that?

[BWRX]

Originally posted by peranders
I have never exeperienced this even with heavy and large boards out there in the industry.

I agree with peranders. You have to really bend a board to get parts or solder joints to break, although orientation and location on the PCB have a big influence on this. Most boards are fairly stiff, especially if the dimensions are under about 4-5 inches a side and the PCB is the standard 0.062in FR4, double sided, 1oz copper. For 0805/0603 types the part itself usually breaks before the solder joints if the pads are the correct size and the soldering is done properly. Ceramic caps are more prone to breaking/cracking than resistors.

[koolkid731]

Is there a better way to solder SMD other than soldering on end and then soldering the other end? Does it pay to dispense solder paste then glue the SMDs on to the PCB, then pass it thru a "reflow" owen.

I use home owen to smooth out the solder joints but I wonder about the use of solder paste. Any wisdom out there?

[thomas997]

Originally posted by koolkid731
Is there a better way to solder SMD other than soldering on end and then soldering the other end? Does it pay to dispense solder paste then glue the SMDs on to the PCB, then pass it thru a "reflow" owen.

I use home owen to smooth out the solder joints but I wonder about the use of solder paste. Any wisdom out there?

Its not really worth it imo unless you use small pitch or no lead parts, then it should be much easier w/ reflow. But if you are already throwing the board in the oven, it would save time.

Tube of solder paste from digikey is ~$50 if you want to try it out. No need to glue the parts down if you are careful.

[BWRX]

Originally posted by koolkid731
Is there a better way to solder SMD other than soldering on end and then soldering the other end?

Paste and a reflow oven is best, but you'd be lucky to have access to a real one let alone have one The next best method is to use paste and a hot air rework station. The next best method is a good old adjustable temperature soldering iron with a chisel tip. Use liquid flux when possible for any method to get good solder joints with surface mount parts and clean with isopropyl alcohol and lint free wipes/cloth to remove any flux residue.

Originally posted by koolkid731
Does it pay to dispense solder paste then glue the SMDs on to the PCB, then pass it thru a "reflow" owen.

Originally posted by thomas997
No need to glue the parts down if you are careful.

Usually glue is used for wave soldering. When heated properly most parts will center themselves when passing through a reflow oven thus no need for glue to hold the parts down.

[koolkid731]

Thx for the replies.

I haven't tried solder paste because of the need to dispense it onto the pads, in small droplets (????) then to place the SMDs, all of them. What if I hit the boards and dislocated some SMDs? I would have to reposition them again, wouldn't I. Plus solder paste seems expensive. I bought some but never got around to use it and it's expired by now, most likely (I haven't dared opening the vial!)

I looked at some sites on SMD soldering. They seem to use just solder wire, like what I still do.

Why should one remove flux with isopropanol? for reliability? to prevent further chemical reaction? (acid attack?)