surface mount soldering techniques

[Richard Principal]

Has anybody got some surface mount soldering techniques

The first way I was taught to replace surface mount parts some years ago
(like 10 years ago).

How to replace surface mount parts.
(1) Take off the old part,
(2) Simultaneously heating and rubbing tined copper braid known as solder
braid using a standard hot iron to soak up any old solder,
(3) Clean up tracks with isopropyl alcohol and tooth brush,
(4) Then apply a trace of solder paste over the copper tracks from a small
syringe of paste,
(5) Then put the surface mount IC on top and blow hot air over it until the
paste melts and solders the part in place.

WARNING
One problem when you take off a part for the first time some people make is
they pull too hard and the tracks come away
THE PARTS ARE NOT HEAVY you just need the tiniest effort to remove the part
when the solder has melted.

One of the disadvantage of using hot air is some times you can easily "blow
off" other nearby components.
and found that one idea might be to use "solder paste & soldering iron"

 

[spiffitz]

At work I hardly use the hot air to place SMDs. As long as the iron's tip is sharp enough it works just fine. I apply solder paste, position component with tweezers, then hold down component in place with tweezers while soldering or else the hot solder will pull it away from the opposite unsoldered trace.

 

[ajc]

I never had good luck using hot air....the best method I found to
remove SMD resistors,caps,inductors,etc. was to use two low wattage
soldering irons...The parts I worked with were so tiny that they
would stick to the soldering iron tip....gently tap your hand on
the bench and the part falls off....total heat time maby 2-3 secs.

To remove IC's we had special nippers imported from Italy...with
EXTREMELY fine tips to very gently cut the legs at the epoxy
of the device. I recently read an article about using #30AWG
teflon insulated wire soldered to one corner of the chip you
wanted to remove...you would then heat each pad on the board
and gently pull the wire between the pad and pin...the author
claimed this method worked great.

Hope this helps...Art

PS....To resolder components use SOLDER-WIK on the
pads....Then(if you can get it)brush on thin coat of
KESTER liquid solder flux...this stuff works like magic.
pretin part and pad...use wooden q tip to hold part
in place...tac solder one side then go back and resolder
both sides or all pins of chip.

 

[spiffitz]

Most of the time I use the hot air pen I end up scorching the surrounding area of the PCB before the solder even melts. There must be a correct way of using it but it seems like a waste of time to me. Tapping each point with an iron for a few seconds works much better and faster.

For two-point SMDs I alternately tap each side with the iron while pulling up with tweezers. Each tap of the iron brings that side up a few .001" (just a guess) and eventually the component will lift right off.

With multi-pin SMDs I very gently pry a leg up with a very sharp X-acto knife or fine-point stainless-steel tweezers while heating that leg. Once the solder melts the leg lifts right off. When all the legs on one side are off, I tilt the component to get tweezers under it, then "rake" the remaining legs with the iron, like strumming a guitar, and they usually all pop off at once.

 

[hjames]

If you have board with heavy ground layers, rework with hot-air pencils isn't going to be easy. The best thing to do in that case is to preheat the entire board - 30 seconds with a paint stripper works well enough. On 2 layer boards, or thin/small boards, they work wonders - nearly no risk of mangling the components or board unless you have the temperature set too high.

If I have to rework a single component, I'll usually just use an iron, but when doing a couple localized modifications, I switch over to the hot-air pencil. The first operation with the hot-air pencil takes a while to heat up the surrounding area - 10-15 seconds, but the successive modifications go quite a bit faster. Plus it's the only reasonable way of using MLF/hidden-pad components.

 

[Westinghouse]

I did a lot of SMD soldering when I worked on mobile phones for about 5 years.
I use hot air with plenty of liquid flux for removal. The trick is to not hold the air gun too close to keep the force of air from moving other components and keep the air moving in circles to heat the surrounding area as well as that will soak up all the heat if you just concentrate on one area. Also to help protect other components I used a few different shaped RF shields that I'd pulled off scrap boards.
Depending on how the PCB was made will depend on how it can handle it. For example the old ericsson PCB would delaminate very easily and a soldering iron was needed whereas the Nokia PCBs could handle a suprising amount of heat. The Nokia PCBs were 8 layers and I think the Ericsson PCBs were the same.
I also found hot air very difficult to use with lead-free solder too.

 

[ectt]

Has anybody got some surface mount soldering techniques

The first way I was taught to replace surface mount parts some years ago
(like 10 years ago).

How to replace surface mount parts.
(1) Take off the old part,
(2) Simultaneously heating and rubbing tined copper braid known as solder
braid using a standard hot iron to soak up any old solder,
(3) Clean up tracks with isopropyl alcohol and tooth brush,
(4) Then apply a trace of solder paste over the copper tracks from a small
syringe of paste,
(5) Then put the surface mount IC on top and blow hot air over it until the
paste melts and solders the part in place.

WARNING
One problem when you take off a part for the first time some people make is
they pull too hard and the tracks come away
THE PARTS ARE NOT HEAVY you just need the tiniest effort to remove the part
when the solder has melted.

One of the disadvantage of using hot air is some times you can easily "blow
off" other nearby components.
and found that one idea might be to use "solder paste & soldering iron"

wish to see the video.

 

[ectt]

At work I hardly use the hot air to place SMDs. As long as the iron's tip is sharp enough it works just fine. I apply solder paste, position component with tweezers, then hold down component in place with tweezers while soldering or else the hot solder will pull it away from the opposite unsoldered trace.

what sort of iron tips you used? once saw technicians could finish a QFP smd chip within 1mins....

 

[ectt]

I did a lot of SMD soldering when I worked on mobile phones for about 5 years.
I use hot air with plenty of liquid flux for removal. The trick is to not hold the air gun too close to keep the force of air from moving other components and keep the air moving in circles to heat the surrounding area as well as that will soak up all the heat if you just concentrate on one area. Also to help protect other components I used a few different shaped RF shields that I'd pulled off scrap boards.
Depending on how the PCB was made will depend on how it can handle it. For example the old ericsson PCB would delaminate very easily and a soldering iron was needed whereas the Nokia PCBs could handle a suprising amount of heat. The Nokia PCBs were 8 layers and I think the Ericsson PCBs were the same.
I also found hot air very difficult to use with lead-free solder too.

usually how thick is the RF shield you used?

 

[ectt]

is your special nippers imported from Italy...with
EXTREMELY fine tips
very expensive?

 

[ericgibbs]

hi ect,
This thread is 6 years old, the OP may not respond

E.

 

[picbits]

Did you really have to bump a thread that was 6 years old ?