[kramer5150]

Quote:

Originally Posted by aerius Rube Goldberg method: Use solderpaste. Trace the pad pattern onto a thin sheet of aluminum, use a fine Dremel bit to cut out the holes. Place aluminum sheet on top of PCB such that the holes line up with the pads. Put some solderpaste on top of the aluminum. Use a credit card or other such plastic card to squeegee the paste through the holes and onto the pads. Carefully lift the aluminum sheet off the PCB. Place the chip on top of the solderpasted pads. Place the PCB into a cold toaster oven. Set the temperature to 375°F and bake for about 5-7 minutes. Turn toaster oven off, open door, allow to cool to room temperature before removing. Presto! One soldered SOIC!

Is this harmful to the chip?... baking it at 375?

 

[Twombly]

Quote:

Originally Posted by kramer5150 Is this harmful to the chip?... baking it at 375?

Perhaps, if it's for that 5-7 minutes.

Y'know, just maybe.

A little.

 

[aerius]

Quote:

Originally Posted by kramer5150 Is this harmful to the chip?... baking it at 375?

Only if you do it too long. My procedure is basically a home version of the automated solder screen, place, and reflow procedure used in industry to mass-produce boards by the millions. In industry the reflow oven is basically a 10-15' long oven with a conveyor belt that carries the boards through it. It's got about 3-14 different temperature zones starting at about 100°F and ramping up to between 350-400°F and then dropping back down to room temperature. The more sophisticated ovens have more temp zones and may use nitrogen gas inside to prevent oxidation & help the solder flow better. Oh, and they can easily cost a quarter million bucks.

 

[Alwayswantmore]

Hi, looking for DIY advice, and this thread has always been very helpful. So here goes...

I want to remove the internal circuit board from my K1000s.
Here's a picture.

The two big blobs of solder to the left side of each screw head is where the PCB is soldered to two pins (terminals).

I have done plenty of soldering as a kid, but never really worked with desolder. I've seen the wicks and vacuum bulbs sold at radio shack. Do you have any recommendations on what I should use to desolder the AKG board?

Thanks for any help you can provide. Kent[/QUOTE]

 

[ATAT]

Id use braid.. sucker is most useful when you can get to both sides of teh board.. in this case you can't.. get a high power iron, put braid on solder, and iron on braid, hold down and you should be done.

 

[threepointone]

Quote:

Originally Posted by aerius Rube Goldberg method: Use solderpaste. Trace the pad pattern onto a thin sheet of aluminum, use a fine Dremel bit to cut out the holes. Place aluminum sheet on top of PCB such that the holes line up with the pads. Put some solderpaste on top of the aluminum. Use a credit card or other such plastic card to squeegee the paste through the holes and onto the pads. Carefully lift the aluminum sheet off the PCB. Place the chip on top of the solderpasted pads. Place the PCB into a cold toaster oven. Set the temperature to 375°F and bake for about 5-7 minutes. Turn toaster oven off, open door, allow to cool to room temperature before removing. Presto! One soldered SOIC!

if you're using solder paste, do you really need the screen? I thought the advantage of using solder paste was that you don't really have to aim the paste at all; you just put a thin strip of paste on the pads, heat it up, and the solder naturally melts and bonds only to the pads. I think I saw a project for soldering one of thsoe really, really small ~50+ pin surface mount chips onto a motherboard, and that's what they did. I'm sure the professional processes have some sort of screen to ensure more accuracy, but i think you don't really need that much work for diy.

 

[headchange4u]

A friend of mine who works with repairing eletronics gave me a great method for solding small chips or chips with a lot of small pins.

Like other here have stated start by tinning one pad and then tack the chip down. Next take a peice of desoldering braid and put extra flux on it. Then you will want to "fill" the braid with solder by heating the braid and feeding in solder in until it is well coated.

All you have to do then is put flux on the pins/chips that you want to solder and lay the "filled" desoldering braid across the pins and hit it with your soldering iron for a couple of seconds. Solder will flow from the braid onto the pads.

The great thing about this method is that it's not messy like flood and suck, it applies the perfect amount of solder and it helps to keep from bridging pins.

 

[threepointone]

I've been using a book from the library for reference on this, Quality Hand Soldering & Circuit Board Repair by H. Ted Smith. It lists four methods for soldering SOIC chips:
1. For the most part the same as the tack method. I haven't tried it, but it says that you don't really have to bother with a blob of solder; you can just melt the tinning on two of the pads to tack it down temporarily. I would imagine that this would make aligning the chip slightly easier. Then you pretty much flux and solder the leads. He specifically recommends .25mm solder for this. It also recommends soldering every other lead at once to reduce the chance of heat damage.

2. Some sort of method with a special scooped out / single-sided iron tip. I doubt most of us would have this tip, but it pretty much involves drawing the solder across the leads with the tip instead of soldering each one.

3. Apply solder paste in a continuous line at the outside edge of the pads on each side, and use a hot air handpiece to melt it one side at a time.

4. pretty much #3, except using a handpiece that can apply heat to all the leads at once.

No one seems to have mentioned this yet, but there's a section warning about how easily ceramic smt capacitors specifically can be damaged without proper care. There's a huge difference in the thermal coeficient of expansion between ceramic capacitors, the board, and the metal inside the capacitor, so it recommends using solder paste/hot air or preheating the capacitors/board. I don't think many DIYers have this equipment, so I would take this as a warning to solder ceramic smt capacitors as quickly as possible and solder at lower temperatures if possible.