AmpCasq: an OPA1622 integrated headamp project

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#29
adydula said:
Thanks for the suggestion John....is this one ok?

https://www.amazon.com/Kester-951-Soldering-Low-Solids-No-Clean/dp/B004X4KOWS

Alex
Click to expand...

Alex

Please find some inputs based on my experience:
I decided to go on this project after having watched some videos on YouTube. These video did let me think that DFN packages (TI call them VSON or WSON) soldering was within my reach.

First video set the method: you heat the chip under the board assuming you have designed the pcb footprint of the chip with thermal vias (big one) under the chip pad (As OlegSh did notice in post#18). For the project I've designed 3 footprint in Kicad for the 3 chips with such vias.

Second video propose to use solder paste rather than ‘presoldering’ as on the first video (do not add flux to paste, as paste should already contain flux). Advantage is that solder paste allow you to precisely position the chip at the right place and keep it in place if you accidentally breath on it (LM27761 is 2*2 mm ! 🙄). You may also use paste to solder SOIC, 0805, etc. it allows you to control the amount of solder and to keep parts in place. Second video use hot air, as I didn’t want to invest in air gun that’s why I choose to mix the methods of the two videos.

I’ve also invested in a stand which allows to solder underneath the board.
You also need flux (flux is everything says the guy form EEVBlog !) and good solder wick. I had to unsolder many times the LM27761, flux is mandatory for this. The main issue with those tiny chips when you’re making prototypes is that when you encounter a problem, you never know if is due to the circuit (the design) or the solder of the chip. So I did unsolder the LM27761 many times before really suspecting the design, in my case the Pcb layout around the LM27761 was bad...


First video: https://www.youtube.com/watch?v=d-f-SBC0GrU&index=2&list=WL
Second video: https://www.youtube.com/watch?v=M_rO6oPVsws&t=31s
The stand: http://www.ebay.fr/itm/Support-de-circuit-imprime-3eme-main-PCB-plaque-dessai-soudure-montage-platine/111752564162 (in french but available in many ebay, Ali…shops)

Hope this help
Regards

 
#32
Thanks for the help and those videos, seems like I can do the first method ok. Flux, apply solder, clean up reflux and place and heat from the back side to solder.

The hot air tool really looks like a neat way to go, $50 or so for a hot air blower gun and leaded solder paste...very neat!

Alex
 
#33
As others have mentioned, if you go the solder paste route, no need for flux. I haven't done the hot plate for reflow yet. Funny thing, although I have access to a very nice reflow oven at work, 99.9% of the time I just use a weller pyropen and get good enough results. Occasionally you have to touch up the pads with an iron if they get bridged by solder paste, but its rare. Surface tension is an amazing thing!
 
#37
adydula said:
Thanks for the help and those videos, seems like I can do the first method ok. Flux, apply solder, clean up reflux and place and heat from the back side to solder.

The hot air tool really looks like a neat way to go, $50 or so for a hot air blower gun and leaded solder paste...very neat!

Alex
Click to expand...

Applying solder with iron doesn’t leave the surface plane, this create solder bump on the pad, thus it's difficult to have to chip well placed on the board, in addition the chip could easily slide and move. With solder paste applied with syringe, the chip is maintained by the paste which is adhesive. Then surface tension do the fine positioning job for you.
 
#38
The hot air gun method seems the best....I did watch a few videos where they used solder paste and used a small cooking oven and it worked as well....but you would have to set the temp and try a few times to get the temp in the right range, where as with the hot air gun you can see the magic happen before your eyes...

Think I will go shopping for a hot air gun / blower.

Alex
 
#39
adydula said:
The hot air gun method seems the best....I did watch a few videos where they used solder paste and used a small cooking oven and it worked as well....but you would have to set the temp and try a few times to get the temp in the right range, where as with the hot air gun you can see the magic happen before your eyes...

Think I will go shopping for a hot air gun / blower.

Alex
Click to expand...

I agree, I will buy one.
The oven or plate are ok to solder all the parts at a time but, I think, If may be difficult to do some rework on only a chip or when plastic parts not designed for this are used. This is critical for prototyping.
So flux, binoculars and hot air gun should be the perfect kit
 
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