CNC Soldering and PCB Population Tips
Hi all,
Please read this:
I was going to put this in with the CNC PCB packaging but since it's a few pages I decided to post it here.
For most simple PCB's it's easy to just start putting in components, it's best to do it in a logical order, here is how I do it:
Here is the suggested order for installing the components, please read the soldering tips before hand if necessary.
Resistors, these are closest to the board so we will install them first, it's a good idea to double check the values with a DMM. And that the value is the same as on the board.
The component leads of resistors need to be bent at right angles so the leads are parallel to each other with a distance of 9 - 10mm between them. Feed the legs through the holes and bend outwards slightly so they can't slip out again. You can do a couple at a time, it may be quicker to do them all at once but it's harder to solder with all those leads sticking out of the solder side of the board.
Op amp sockets, be sure to place them so the cutout end matches that on the PCB and they go in the center of the board. Gently push them so the pins go through the holes, you can lay the board component side down on a flat surface to keep the sockets hard up against the board.
Dip Switches, make sure the end with the number "1" on it goes to the number "1" printed on the silkscreen and gently push them so the pins go through the holes.
Capacitors, do the smallest ones first, gently push the leads through the holes making sure you have them in the right spot. Electrolytic capacitors in this case are polarized.
The longer lead is the positive lead and must go in the hole next to the positve symbol. The negative lead is on the side of the stripe. Double check polarity of the four 10uf capacitors before soldering. The other capacitors can go in either way round. Gently bend the legs outwards as you did with the resistors so they don't move. Try and have them as upright as possible.
RCA Jacks, you can use any good quality copper insulated wire, color coded is better and 20 gauge is sufficient. Make sure you have the positive lead connected to the center of the RCA Jack and the negative lead to the outside tab.
Power connection, 20 gauge is sufficient here also, we are using batteries and they should be wired as shown in the notes I sent, with positive going to the positive input on the PCB. Negative to negative and the center lead to the G or Ground connection.
Switch, it has to be wired as shown, with only the positive and negative battery leads used and it must have twin circuits. It will have two sets of in and out terminals. The center lead/ground goes straight to the PCB.
LED, is wired as shown with a 8.2k resistor (this value will reduce current draw, if you want a brighter LED you can lower the value but batteries will not last as long) from the negative or shorter lead to the negative wire on the PCB side of the switch. The longer lead goes to the positive wire on the PCB side of the switch.
Ground connection. The ground lead from the batteries/pcb is the ground for the case and turntable and is wired as shown.
Op Amps.
The end with the crater and/or cutout must go to the end with the cutout on socket. If you reverse them they won't work again. Touch something grounded before handling them. I gently place one side of the pins in the socket and using a fine blade screwdriver to gently push the pins on the other side in far enough to fit in the socket. Then push gently down on the top of the Op Amp so it fits snuggly in the socket. Don't force them in.
Now double check your work and connect it up for a test, hopefully you will have sound in both channels. I found mine took a good 30 hours to break in.
Enjoy!
Soldering Tips for Components
I use 60/40 lead/tin solder, I can't stand lead free solder, it's much harder to use IMO.
I also use a small desk fan to blow the flux fumes away as they can cause respiratory and eye irritation as well as a light/magnifier, your eyes might be perfect, mine are old.
Heat the components. This is the critical part of soldering, since good heat conductivity needs both solid contact and pressure. Place the tip of the soldering iron so it's touching the solder pad first then move it so it touches both the pad and component lead and apply gentle pressure. The pads are part of the PCB and take a little longer to heat than the component leg. Both the solder pad and the component lead must be heated to a temperature high enough to melt the solder. If only one of the surfaces is hot enough, the solder will not form a correct bond and you'll get a cold solder joint.
Apply some solder. Touch the solder to the component lead and solder pad at the same time, but do not touch it to the soldering iron tip. Keep feeding solder into the joint until the space fills with solder.
Take the solder away from the solder joint. Be sure to do this before removing the iron or the solder may solidify and stick the solder spool to the solder.
Take the iron away from the solder joint. The entire process from the moment you heated the components to this step should have taken no more than a few seconds. This takes some practice to get right.
Examine the solder joint. The liquid solder will solidify in a second or two. Once solidified, the solder should form a "shiny tent" of solder over the joint. It should not be bulging, bulbous or uneven. If it's not shiny or has cracks that look like a spider web, the solder was not hot enough. Place the tip of iron on the joint again to remelt the solder.
Clean the soldering iron tip prior to each joint. To clean it or remove excess solder, roll the tip on a damp sponge or a proprietary iron cleaner.
Cut the component lead off just above the solder joint with wire cutters, be careful not to cut the joint itself. Be sure to keep a finger on the component lead as these can easily fly off and hit you in the eye.
Wait for the soldering iron to heat up again before doing the next joint. Every joint you solder will cool the soldering iron down a little, depending on your iron this time can vary. If you don't let the soldering iron to heat up again, you'll make cold solder joints.
After all soldering is complete you can remove excess flux on the solder side of the PCB with a toothbrush dipped in 91% alcohol, shake off excess alcohol before gently brushing the solder side of the board and allowing to air dry.
Also check the board for solder bridges, these are where traces or pads on the board are shorted out by having too much solder. You need to use a solder sucker or solder wick to remove the excess.
PS
lease wait a while like 5 minutes after plugging in your iron if it doesn't have a temp setting.
If in doubt ask questions.
.
