I have worked with 0402s (and I have a very limited stock of them) but I hate to use them. I probably lose about half of them which I try to mount. Often they get lost in the drop of solder on the tip of the soldering iron. My “default” is to use 0603’s on a small 0805 footprint. You can really put an 0805 on that small 0805 footprint, but I have a bigger 0805 footprint for when I really want to use an 0805.
15 posts were merged into an existing topic: First design - looking for feedback
A bit of manipulating posts, but now seem to be in correct time order. 
Thank you @Piotr, @BobZ, your feedback came in a timely manner as I was soldering the 5 SIPO ICs…
It’ll get very busy in a moment there wiring everything up with jumper cables and I don’t think it’d be as easy to add the 100n caps as I did now…
There is a problem with modern ICs. Manufacturers try to manufacture them as cheep as possible. So for even the old chips they use modern (much smaller) technology to shrink the semiconductor wafer area used for each IC. The effect is that even the IC that according to datasheet is not very fast can be fast. That means higher and shorter current pulses taken from power lines and greater sensitivity of the inputs to short pulses that the old IC would not even notice.
This is not a problem for combination ICs (like decoders, multiplexers) but it is a problem for ICs with state dependent on pulse history.
In 93 we designed some education system with serial EEPROM connected to it by 10cm flat cable and everything worked. In 2006 we bought several hundred of EEPROMs (same manufacturer, same type) and they didn’t worked. The reason was - in that 10cm flat cable their output slope crosstalked to their clock input - each (one direction) output slope effect was extra +1 in their clock input counter. The output slope was faster than in 93 and clock input was more sensitive than in 93. It was deterministic behavior, not random. We could count how each byte output was corrupted by skipping some bits.
From that all my opinion is: Your circuit should work, but there is (I hope less then 1%) chance it will not work assembled that way and will work assembled with SMD ICs at designed for it PCB.
What I want to say: Use power of KiCad, Luke!
Those thick PVC insulated wires are nice for working on breadboards, but on Perfboard it’s a horror to work with. Sripping the wire ends becomes a bore quickly, and when the PCB gets more crowded it’s easy to damage the insulation of nearby wires during soldering. I know because I also did that 30+ years ago, but quickly learned otherwise. I prefer to use 0.2mm “enameled” wire. (and thicker for currents >200mA) in combination with a soldering station that can be set to slightly higher temperature which is needed to burn of the isolation.
In an older version of my method I used to stick the 0.2mm though the PCB, then bend them around pins with the tip of a knife and cut them with the same knife. After that the wires stay in place (so you can first lay a lot of wires) and then solder them.
A quicker method is to keep the wiring on the bottom of the PCB, but then it’s more vulnerable to the hot soldering iron. A good method is to buy a second soldering iron. Then use a hot iron only for burning off the isolation and tinning wire ends, and the other iron a bit cooler to solder the wires to the pads. With this cooler soldering iron, you won’t damage the insulation even if you touch other wires accidentally.
been there with my first small projects… I bought Silicon insulated cables (what you see on my SS) so that eliminates the insulation damage by the hot iron, they are a pleasure to work with…
I am considering the enameled copper wires but am afraid of working with them as i don’t know how to…
So, since you’re experienced on this, can you be more specific as to what is a “hot iron”?
I work with 315c now… what temp would be enough to burn the isolation?
And most importantly: How do I verify that the isolation has indeed been burned? That’s the most frightening aspect to me to working with enameled wire, that I won’t be able to verify how much insulation I’ve burned and have shorts…
I have worked with 0402s (and I have a very limited stock of them) but I hate to use them. I probably lose about half of them which I try to mount. Often they get lost in the drop of solder on the tip of the soldering iron. My “default” is to use 0603’s on a small 0805 footprint. You can really put an 0805 on that small 0805 footprint, but I have a bigger 0805 footprint for when I really want to use an 0805.
In most cases I don’t mount our PCBs myself. 0603 I use at their standard footprint (no way to use 0805 there). During last 5 years about 3 times I had to experimentally find the best capacitors for RFID antenna. Values obtained from theory work good if you want to read not crypted card. But when we had to use crypted cards they need more power for their processor and read distance reduces dramatically (for example from 4cm down to 1cm). You have to look for optimum at final circuit (any difference counts). So for example I assembled C1=C2=10pF and than changed C3 from 130pF til 160pF every 2pF. Then I changed C1=C2=12pF and once more all values at C3 and so on for C1=C2=10…30pF. It took me 2 days to continuously disassemble and assemble 0603 capacitors. PCB withstood it but changed the color a lot 
To disassemble 0603 I use 2 irons (one of them is 100W transformer). When I pick up capacitor from PCB I switch off transformer iron and capacitor stays at it. Then I put the second iron at its place, take tweezers and get capacitor from transformer iron switching it on for a second. Then I check the value with RLC bridge and put it into right Tic Tak box (nothing can go to waste ).
Wow! Amazing technique but I think I am missing something. When you pick up the 0603 between two irons, that requires two hands, correct? So if you then want to switch off one of the irons, doesn’t that require a third hand? 
Have you ever seen the transformer iron?
It has a switch like drill.
In 1980 at the way back from our student expedition to the mountain rivers of Yugoslavia (my avatar is my photo from that) we stopped for one hour in Czechoslovakia right next to an electronics store and I spent all the money I still had on a transformer soldering iron. I still have it. Its switch was working very hard (highly springy plate). You had to press it so hard that your hand immediately began to twitch. So I at once replaced it with microswitch and since then it is hard to keep it in hand and not to switch it on.
Ahhh, OK. Are you referring to what we call a soldering gun? I think of this as being too big and powerful for delicate SMT work.
https://www.weller-tools.com/bigbang/USA/us/Soldering+Guns
I still have mine from about 1965. It still works but finding the right tips for it can be a challenge. I use it when I need more heat for bigger soldering jobs.
That criticism applies to my cheap reciprocating saw. It is certainly good for its price, but the biggest problem is to switch it off while still holding it.
But good for separating panelized PCBs???
Only if you do not care about sawing straight lines! I use it mostly for tree branches between maybe 3 - 10 cm in diameter.
I am reminded of a saying from a former electronics co-worker: “Measure with a micrometer, mark it with chalk, and cut it with an axe.” I guess a reciprocating saw would be slightly more accurate than the axe, and a chainsaw would be similarly accurate with the axe. The chainsaw would be the fastest and most dangerous.
I thought you bent a piece of copper wire to form a tip for those guns.
We (in Au) had a more civilized version of your solder gun.
Basically the same as your gun but the 3VAC 30A output transformer is on the bench top.
This iron is held like a pencil and your fore-finger operates the lever switch.
Performance: Cold to glowing red tip in about 12 seconds.
I was a bit surprised to see them still for sale… mine dates back to about 1970.
The other thing…All but the cheapest soldering irons have a transformer in the base unit and operate the heating element at low voltage. So I had no reason to thing that a “transformer iron” was any different. Also my hands are unsteady. I would likely bend the tip of my soldering gun if I were to try to hold a chip component between the tip of the gun and the tip of another soldering iron.
Dated, corny and unhealthy joke:
Did you hear about the chain smoker?
They went back to cigarettes.
I’ve blocked the Bob guy because I find it quite annoying he derails so many threads with what he apparently thinks is funny. I also sent him a few pm’s about this some time ago, but he doesn’t care.
To me it now looks like:
Back to the topic:
Indeed, silicone isoalated wire is much better, as it survives your soldering iron. “Kynar” (=Teflon) insulated wire apparently also works well, but it’s also very tough and hard to strip. You can strip silicone wire with your nails because the silicone is not very strong mechanically.
I usually have my iron set at around 400c but it’s a compromise. A hotter iron has a bit more tip wear, and the flux evaporates more quickly. I just did a test and the insulation starts melting at around 340c. There are also different sorts of coatings used for enameled wire and those cook off at different temperatures. To do this you really need an iron with an adjustable temperature, and then just try what works best for you.
It’s quite easy to see actually. The solder does not stick to the coating, and as soon as you see the solder wetting the wire, you know the isolation is gone. The coating also makes it more difficult to heat the wire. I discovered that if you start by applying solder to the very end of the wire, then the cut cross section wets first, which speeds up heating of the wire. Everything together it works best if you first apply a very small amount of solder to the very end of the wire to create a thermal connection, and then, when the isolation cooks off, you apply more solder, which also has fresh flux, because the old flux has evaporated before that.
Also, the coating is transparent, so you see the red copper color. Once the isolation is gone and the copper is wetted, the wire has the whitish tin color.
A difficulty with this method is that the IC sockets can get too hot too and the plastic melts and deforms. Heating just the wire end first (so not even touching the socket pin or the pad) helps here too.
But as with all new methods, you will need some experience. I suggest you just get some and try it. 0.2mm is good enough for all connections up to a few hundred mA. I never tried thinner wire (0.2mm was the thinnest I could get locally, (It was from before internet existed)) For higher currents I use wire from a degaussing coil from an old CRT. There is a lot of wire in one of those and its about 0.5mm
If the source of heat is the current flowing through the tip we call it transformer iron, others are standard (heated by resistance heater). Mine has the tip mounted horizontally and it is the key feature. I can’t imagine how I could use the ones from your picture to desolder 0603. A wire bent vertically will not touch the pad well.
I use that iron also to magnetize or demagnetize screwdriver or tweezers.
I use copper wire. In past I have made many tips with special shapes to heat at once all pads of 1206, 0805, SOT23, SOT323, SOT23-6, SO8, SO14 and others but I didn’t used them since years.
It’s eternity.
I have one without base station (directly heated from AC230) and it is not the cheapest one. It has temperature setting knob in the handle, and many interchangeable tips offered.
I will second the recommendations of @paulvdh – enameled wire is the quickest and easiest way to hack a pcb or wire stuff on a perfboard. I got a red and green roll of AWG 28 (~0.32mm) which is a nice size for me to work with (and some thicker stuff for power). They make high-temperature enamels for motor windings and such, so you need to get low-temp stuff, but it easily tins with my iron at 400C. Clean your tip often. I also use two irons for removing parts; it’s not that complicated as the part will stick to one tip or the other or just drop off, but it is easy to remove an smt passive with two irons. For gull wing parts, I use a new blade in an xacto and push down to slice the pins next to the body until the body falls off (careful to not hit traces under the chip), then wipe the pins off with an iron, and tidy up the pads with solder wick. I have a hot-air gizmo but it is more hassle to set up and use.
