SMT help

[zachtheterrible]

I have ordered the parts to make my ultrabright LED flashlight, and most of the parts are SMT. I had no prior experience with SMT until yesterday when I whipped out an evaluation or practice board that came with a bunch of SMT stuff. I got it for free from someone in the electronics industry, i love having connections :lol:

Anyway, I'm not sure if I'm doing it right.

For capcitors, resistors, anything in the little rectangle packages, this is how I do it: I hold the piece in place with tweezers and put my solder tip with a bunch of solder on it up to one side of the package and let it adhere to the board and component, then do the same to the other side. It seems to work very nicely.

For ICs: I take my solder flux pen (also a freebie :lol: ) and "draw" over all of the solder pads. Then I hold the IC in place with tweezers and drag my iron loaded with solder over all of the pins. If there is any bridges, I take and clean 'em up with solder wick. This also seems to come out very nicely.

In my evaluation kit I had some kind of graphics processor with 120+ pins. I used the process decribed above to solder the thing in and it came out pretty well, apart from it's probably being fried because I took too long on it.

A few questions:
1. Just how much heat can those tiny little things absorb and not be destroyed? With through-hole components, youve got the leads which act as sort of a heatsink, and whever you solder it in, the soldering iron is not right next to the component.
2. Do I really need to tin my boards before I solder things in? I think that tinning is just so that the board doesn't oxidize. If I make the board right away and solder everything, then it won't have a chance to oxidize. My evaluation board was pre-tinned, and I'm not sure how much of a difference that made.

I looked for tutorials on SMD on google, and there is a surprising lack of them. Thanks for the help :lol:

 

[instruite]

There was discussion of how to solder Surface mount components before
If you go by my method mentioned in that thread (obvioulsy do use flux and other stuff) touching the solder iron to the device can easily be prevented

and regarding the specifications of how much Soldering temperature IC can handle then it depends on the MSL (moisture sensitive level) of IC
you can refer standards J-STD-20C or any equivalent standard for exact details

 

[zachtheterrible]

Hey instruite, I did a bit of searchng and couldn't find the article you were talking about.

Just how can it be done without touching the iron to the component? Other than using the oven reflow method, which is out of my reach because my mom would never let me :cry:

 

[mstechca]

A few questions:
1. Just how much heat can those tiny little things absorb and not be destroyed? With through-hole components, youve got the leads which act as sort of a heatsink, and whever you solder it in, the soldering iron is not right next to the component.
2. Do I really need to tin my boards before I solder things in? I think that tinning is just so that the board doesn't oxidize. If I make the board right away and solder everything, then it won't have a chance to oxidize. My evaluation board was pre-tinned, and I'm not sure how much of a difference that made.

1. how about minimal heat. As soon as the component is soldered, remove the heat immediately.

2. You should at least give your board some heat. from the iron, and make it clean so that solder can be applied.

 

[instruite]

Hi
I think I didnt made a clear statement
By not touching the component I meant by not touching the package of the component
You have to touch the pins atleast if you are using a soldering iron

here is the discussion link

https://www.electro-tech-online.com/threads/jdm-type-modification-by-someone-electro.16389/

Its basically applying solder at the pin pads on PCB and then just placing the component on the pads and touch(some times you may have to press the pins a bit also) the pins with the soldering iron (without any solder on it) Since you dont have to worry about solder you can easily solder all the pins without touching the package at any time. (I have succesfully used this method to solder 256 pins microcontroller ics )

 

[zachtheterrible]

Thanks for the link instruite, it sounds like ive already got the right idea.

One more question though: In regular through-hole soldering, I always keep a blob of solder on my iron, and then when I need to solder something, i wipe it off and put new solder on there, so as not to let the tip oxidize. In SMD, you can't always have a blob of solder on the tip. Should I worry about that?

 

[instruite]

Hi zachtheterrible

These is no need to have any solder on the TIP of solder iron when you are soldering the SMD package
The solder is put on the pads on PCB before placing the component and no extra solder is required after placing the component just enough heat to for the solder on PCB to melt and get attached to the pin of the IC

 

[pittuck]

i recently did some SMT soldering with an soldering iron and my standard solder.

For small resistors i put blobs on the pads, hold the chip down with a reistor and heat the pads (have a bit of solder on the tip). For a chip (was SOIC) i put solder on one pad, place the ic and melt solder. I wait ten seconds or so fot it to cool then reheat and reposition the chip. Then on alternating corners i solder them. (alternating so not to heat up the chip too much). Finally i have some electronics cleaning solder which tidies up the mess of flux and stuff on the board .

For timing, 3 seconds is what i have always been told. Double the time for cooling.

 

[zachtheterrible]

Hi zachtheterrible

These is no need to have any solder on the TIP of solder iron when you are soldering the SMD package
The solder is put on the pads on PCB before placing the component and no extra solder is required after placing the component just enough heat to for the solder on PCB to melt and get attached to the pin of the IC

I'm not questioning that part. I was thinking that the tip of my soldering iron is going to oxidize because I don't have any solder on it.

I was always told to have solder on the tip of my iron when it is on.

 

[instruite]

zachtheterrible:

I'm not questioning that part. I was thinking that the tip of my soldering iron is going to oxidize because I don't have any solder on it.

I was always told to have solder on the tip of my iron when it is on.

Sorry I interpreted your question in a different direction before

I never had any problem of oxiditation by keeping the soldering iron without any solder on it
But I do have a water spunch in my soldering iron stand and I normally move the tip over it so as to clean the solder tip

 

[audioguru]

I have had the same tip on my Weller temp-controlled soldering iron for years, and it hasn't oxidized nor worn out (yet). I clean it after a few solder joints by wiping it on a damp grooved sponge. The grooves collect bits of excess solder and flux and the tip ends-up clean but still tinned. :lol:

 

[zachtheterrible]

Cool, thanks for the help, I guess I don't need to be all that worried about it. :lol: