Anyone in the UK who can do some prototype SMD for me please?

[See_Mos]

As the title says,

I need to make a buck regulator with a very wide input range, from 20 to 100 volts input and 15 volts out.  I have found a suitable IC, the Analog Devices LTC7138.  The problem is that the device is only about 5mm square and the pinout pitch is only 0.5mm. I do not posses the equipment or skills to handle such a small device.

Can anyone help please?

[trastikata]

It's not so difficult See_Mos,

I regularly solder such small and even smaller ICs. I see the IC in question has MSOP pinout - that's very easy to solder.

1. with a soldering iron tin the bare solder pads using lots of no-clean solder paste   
2. the no-clean solder paste will prevent bridging the pads
3. if bridges are present - do nothing for the moment
4. place the IC and adjust with tweezers.
5. press it down and go over the pins with lots of paste
6. go over the pins with the soldering iron and lots of solder
7. everything will bridge in one big mess
8. put lots of paste again
9. place de-soldering wick over the pins on one side
10. put the soldering iron tip over the wick that's on the pins and heat it.
11. the excess solder will be "sucked" by the surface tension into the wick
12. repeat on the other side
13. place some paste again over the pins and iron tip's tip heat the pads from the PCB side - this will draw the solder to the pins, if bridges between the pads (pins) are still present.

Later today I'll make a short video.


use some bare copper wire or de-soldering wick to remove excess solder

[JonW]

How many boards do you need?  We place devices by hand using microscopes and hot air pencils for development.  You can just tin the pads and place it, but if you are not confident, then it's not worth it. 

  If it's a couple I can help you.

[John Lawton]

You're doing it the hard way

Put thick liquid flux all over the pads, use plenty.

(I use Multicomp Rosin Flux from Farnell)

Place the chip on the pads accurately and hold down with tweezers.

Get your iron, clean the bit and apply some solder to the bit so it holds it.

Apply the iron to the pads, wipe it along the line of pads and they will take the solder.

Repeat on the other row of pads.

Inspect and resolder any pins that are bridged or lacking solder

Remove excess flux

You're done.

[See_Mos]

Thanks for the ideas.  Initially I will only need a couple to prove the idea then I will pass the design over to the end user who will probably need quite a few.

The IC current is borderline for the application. It is possible to double up to bring the current up but the IC's are quite expensive.