Placement of resistors.

I did buy some scrap boards from sparkfun and got a few samples to practice with. It was awful.

I did purchase Sparkfuns Heaterizer XL-3000 knowing that it wasn't entirely capable of solder rework and such, although this guy did all this with it.

I'm hoping that it'll be able to help me out with the soldering a bit, especially with the QFN tlc5940

Using the right tool helps alot, but alot of it is practice id suggest practicing on similiar size smd parts before you go for broke with the ones you bought I collect all sorts of scrap boards, some of it very dense smd boards I wipe them entirely clean with a toaster oven and sort out the smd parts, then when I want to practice I take the newly cleaned board and try to resolder the parts, its great practice

oh wait…can’t I just make a reflow oven? I have an older toaster oven in the basement that we don’t use any more.

Yes you could, just need to control the power to the elements, have a high temp sensor, and maybe a little display to make it all official im planning on doing it with my toaster oven, but not yet as im only using it destructively to remove parts not put them on and so I don't care if the temperature is as 350 or 400 or 450, just so long as the solder melts In a reflow oven the temperature is quite important, as well as following a proper temperature curve which is pretty easy once your controlling the heating element

Okay, I think I'll just do that.

If you don't want to do SMD and you can tolerate 0.1" spacing a bussed resistor network is handy:

I've always been unsure about those bussed networks. Say I connected them to a number of ICs that don't have diodes. What would stop the electricity from going through the network and then have a signal at some random ic that is connected to the bus.

I wouldn't give up on SMD totally though, I absolutely hated it for years, now I can solder it down without even holding the components. I still dont use it for 1 off stuff, its too much of a pain for me to make PCB's since I dont always have the right stuff on hand, but have plenty of perf board

though as someone else mentioned you would be pretty suprised how much SMD stuff can actually fit on .1 pads, like 805's plcc 4's SMA/SMB stuff etc

Well I know they are much smaller and I don’t hate SMD, I just am not good at it. I wish I was better because then I could get the parts, throw it together, and it would work just as well as my through-hole projects and they would be so much smaller.

I used to be scared of SMD - now I use it all the time, even on my own home-etched (toner transfer method) boards.

Fore anything smaller than SOIC pitch I tend to use a breakout board of some form (I have some very nice ones specially designed for 100-pin TQFP PIC chips that include all the bypass caps and an ICSP header), because it's more reliable than using TT.

0805 SMD capacitors at 100nF make fantastic bypass capacitors - they just solder directly between adjacent power/ground pins on a DIP chip. They don't take up any room at all then. 22pF ones also make good load capacitors with a crystal between two outer tracks and a central ground track. Again, no room.

Yes, it takes a bit of practice to get it right, but if you always shy away from it then you'll never get that practice. And SMD passive components are so cheap I don't even worry about dropping some on the floor.

0805 SMD capacitors at 100nF make fantastic bypass capacitors

Whats a bypass capacitor?

bypass - decoupling - they're different names for the same thing.

Ohhh okay.

On a side note, has anybody used the Heaterizer XL-3000 Heat gun and had success doing solder rework?

No, but I have used a 12$ butane hot air pen successfully so I imagine that would work tho for smd ics with more pins than a few I prefer to use the solder drag and wick method, hot air took a while

I've tried the solder drag method before. I ended up with all the pins connected to eachother. I stopped there. Was I supposed to wick away the excess after that?

Yes, bridging is normal before that, the solder wick takes off the bridges leasving just enough under the pins for a good connection

its funny, every time I try that theres never enough solder and I have to go back and reflow a pile of pins ... but if I want to remove an IC with wick, not one pin will pop loose.

not saying the method is invalid, just saying I must be the only one not doing it right

but if I want to remove an IC with wick, not one pin will pop loose.

That is telling you that you did have enough solder in the first place.

MMkay, well I think I definatly have enough solder on there, haha. I'll try to wick sometime.

Btw, since we are on the topic of resistors, can anybody explain what pull-up and pull-down resistors are? I knew at one point although since I've been broke, I haven't been able to really make any of my concepts and I've just forgotten.