AS15F replacement which fluxes?

[Grunder]

Good morning, I have 3 lcd's with milky or white pictures, with the AS15f chip to hot to touch. I have seen two clips on you tube where the chips are changed using a hand held soldering iron. (ouch!)

In the one clip, a lot of clear looking fluid is squirted on during the removal process. Is this just cleaning, or cooling as well? What fluid would be recommended?

The second clip looks like a concoction in a syringe? Could I maybe have a local chemist mix up something?

[dick_barton]

Re: AS15F replacement which fluxes?

The make of flux does tend to be a personal choice. Some fluxes appear not to boil away too quickly or leave a heavy residue behind. Some also come in a syringe which can make it easier to spread the flux only where you want it.

Isopropyl or something similar is sprayed on afterwards to remove the flux residue prior to fitting the new device. Fresh flux and fresh solder is then used at this stage.

Suggest you practice on an old board.

[Grunder]

Re: AS15F replacement which fluxes?

Thanks Dick, have plenty old boards with same/similar IC to practice on. Will google fluxes and also ask my delivery guy what the other gents are using.

[dick_barton]

Re: AS15F replacement which fluxes?

There is an added difficulty in removing the AS15x chips if the base of the IC is soldered onto the copper below it. Requires more heat to dislodge it while being careful not to overheat and damage the tracks. Something I am familiar with doing myself.

[diif]

Re: AS15F replacement which fluxes?

I've used Chipquick to help remove them in tje past, although I prefer hot air now.
I use genuine Amtech 559. Flux with a needle to dispense it accurately.
Not the cheapest but doesn't dissapear at the first sign of heat.

[dick_barton]

Re: AS15F replacement which fluxes?

The hot air gun is definately a plus but do not put the airflow up so high that it blows the very small smd's off their solder pads. I've done that too.

[Alastair E]

Re: AS15F replacement which fluxes?

There is an added difficulty in removing the AS15x chips if the base of the IC is soldered onto the copper below it. Requires more heat to dislodge it while being careful not to overheat and damage the tracks. Something I am familiar with doing myself.

Nah--No problem!

Cut the pins off chip with Stanley-knife then remove them with solder and iron.

Ping off chip with blade under edge, simple, easy quick.

clean up board, coat with home-made flux, on with new chip drag-soldered.

All done in 10 mins, and no hot-air in sight.

[dick_barton]

Re: AS15F replacement which fluxes?

Excellent suggestion Alastair E and already filed away in my head but won't pinging off the chip rip up the copper pour below it.?

[dick_barton]

Re: AS15F replacement which fluxes?

Nah--No problem!

clean up board, coat with home-made flux, on with new chip drag-soldered.

All done in 10 mins, and no hot-air in sight.

Drag-soldered. Do you mean running the soldering iron tip preloaded with solder along the legs of the IC.

[Alastair E]

Re: AS15F replacement which fluxes?

Err--No, and Yes in that order!

Just occasionally the top will leave the chip die on the board,when you ping it off, but simple iron and solder takes care of that...
--Important NOT to drive the blade under the chip case, doing so could cause damage. you can get enough grip just by resting blade edge under the chip with no shoving.

[dick_barton]

Re: AS15F replacement which fluxes?

Thanks Alastair E for an excellent hint.

[stj]

Re: AS15F replacement which fluxes?

as15 does not always have copper heat-spreader under it, check the part number agains the datasheet - there are several versions.

[ReeceyBurger123]

Re: AS15F replacement which fluxes?

As15 H has a heat pad As15 F does not. Also flux does not matter any type will work, its your skill at soldering when it comes to this type of work.

[dick_barton]

Re: AS15F replacement which fluxes?

Hello STJ,
The ones without the bases soldered to the board are not a problem. It's the one which are that I find a pain. However I do like Alastair E suggestion to remove the legs first and then I can concentrate my heat gun onto the body of the IC without worrying about damaging any tracks when lifting it off the board.

[Alastair E]

Re: AS15F replacement which fluxes?

As15 H has a heat pad As15 F does not. Also flux does not matter any type will work, its your skill at soldering when it comes to this type of work.

Aye--Even my home-made colophony concoctions....

[ReeceyBurger123]

Re: AS15F replacement which fluxes?

Hello STJ,
The ones without the bases soldered to the board are not a problem. It's the one which are that I find a pain. However I do like Alastair E suggestion to remove the legs first and then I can concentrate my heat gun onto the body of the IC without worrying about damaging any tracks when lifting it off the board.

You dont even need to do that. I just use flux and hot air for the ones with the heat pads works just as well never damaged a trace. Will be doing a youtube video soon.

[dick_barton]

Re: AS15F replacement which fluxes?

its your skill at soldering when it comes to this type of work.

And that's what it finally comes down to. I need the practice.

[Alastair E]

Re: AS15F replacement which fluxes?

Flux, flux--And More flux--you can almost never have too much!

[ReeceyBurger123]

Re: AS15F replacement which fluxes?

Flux, flux--And More flux--you can almost never have too much!

Too true, flux is your best mate when it comes to work like this !

[Alastair E]

Re: AS15F replacement which fluxes?

The good bit about the Colophony based type flux is you don't really have to clean it off after work-- unlike the gloopy greasy types commonly available (which I dislike), Its just like the original stuff already all over the boards anyway!

Only place I do clean it off well is on Buffer-chip pins, that then get coated with ulti-meg...

Easy (and cheap--I like Cheap!) to make--Take some colophony resin and dissolve in alcohol to make a strong amber coloured fluid--If you add too much colophony--it goes milky, but still works fine, but you can add a little more alc to get the clear amber back....
--I use an 'e cigarette' fluid bottle to store and apply, has a short and thin spout just right for application.