@ian field
I know what you mean. I've posted here a video describing (in the second part of it) exactly what you wrote.

@SLK001
I would use the hot air gun technique. This means that I need the device, the special paste, paste dispenser, liquid for washing, special fluid flux, etc. (mainly from american Chipquick company).
Before ordering that stuff I will check your "double-iron" technique when the ordered SMD parts will arrive from Digikey.

About PTH caps, I was thinking that they are ok for "big" capacitance like 1uF or more, but I have some doubt about the 0.1uF one, as well as about the 30pF cap (near the crystal oscillator).

 

Unless you are planning to use SMD adhesive to bond the parts to the board prior to your hot air "reflow", I wouldn't recommend using hot air. I had a Hakko hot air soldering station that I got rid of because of "disappearing" parts. If all that you are going to use is an uncontrollable air speed heat gun, then you are going to disappoint yourself - plus loose a lot of parts.

Even the 0805 sized parts will get moved around quite alot. The 0603s and the 0402s are like grains of sand. They will get blown off the board and lost forever.

 

They will get blown off the board and lost forever.

Maybe this the real reason why SMDs are sold in such big amounts in the electronic market.

This is the reason why I'm going to use:

1. the sticky solder paste (among other products) from Chipquik - I see only excellent review/opinions around about this company.
2. big 1206 SMDs (i.e. 3216 Metric) - so I can keep parts in position with tweezers (if necessary).
3. low air-speed (just like in the video I posted here).
4. Pb added solder (melting point at 183 C°)

edit: I would go with bismuth-added solder (melting point at 138 C°) but many people said me that this a risk when/if the component absorb a lot of current and became hot.

 

Hello,

Just found an old PDF on my disk.
Perhaps that would give you an idea for RF decoupling.

Bertus

 

Hello,

Just found an old PDF on my disk.

Just seven pages. Pfeeeeew! My marriage is not gong to be broken...

 

That (interesting) PDF is primarily talking about radio applications (i.e. frequencies in the scale of Gigahertz) while my case is far below the 20 Mhz range.
I remember old radios: if you look inside with attention you can discover many disc-shaped caps flying in open air; with one leg soldered at the chip pin and the other soldered on the board.

Anyway, I still have to see one serious paper (with numbers, no talks) confirming the supposed absolute total superiority of SMD caps vs traditional leg-mounted ones (while the cap structure is the same in both cases). The massive plates at both ends (that are necessary to solder them) should produce more parasitic inductance then a short wire.

 

Just chiming in that one possibility for a hot air gun is to get an embossing tool from a craft store. It's intended to melt plastic powder for embossing, and does not have as strong an airflow as a regular "hair dryer" type hot air gun that you would find at a hardware store. A hot air station is better, of course, with airflow and temperature control, but the embossing tool tends to be inexpensive. Even if you do most of the soldering with irons

you can still use hot air and some liquid flux to anneal the connections, especially on IC's.

 

Thanks Roderick, your video explains the "two-irons" technique very clearly. Very good video!

What solder are you using? With lead (melting point 183 C°) or lead free (melting point around 217-221 C°)?

 

Thanks Roderick, your video explains the "two-irons" technique very clearly. Very good video!

What solder are you using? With lead (melting point 183 C°) or lead free (melting point around 217-221 C°)?

In this case, mostly 63/37 lead/tin solder. It's the same roll I've had since the late 1970's. In a few cases, I'm using 60/40 solder with a finer gauge, because I happen to have a coil of it lying around from an old Heathkit of the same time frame.

The embossing tool works fine for melting this solder if I want to reflow joints to make them look really nice. I don't know what it would do with solder of a higher melting point.

The general question of what solder is best is an extended controversy, and I don't want to start a fight in this thread.

 

Back to the bypassing issue, at work, we had similar almost-impossible issues meeting the manufacturer's requirements for bypassing certain processors. We would work with the manufacturer, and they would approve a bypassing layout, and components. Eventually, the manufacturer simply started releasing a recommended bypassing layout for everyone to use. Sometimes what they mean is that they need ten 0.01 uF capacitors in parallel, each in a strategic area, rather than one 0.1 uF capacitor somewhere. If your chip is really picky about bypassing, perhaps their application engineer has such a recommended layout already available.

 

If your chip is really picky about bypassing, perhaps their application engineer has such a recommended layout already available.

Still waiting an answer from their engineers. No signs of life from that side...

 

Thanks Roderick, your video explains the "two-irons" technique very clearly. Very good video!

Not quite... Between the application of the solder and the placement of the parts, you should ALWAYS apply paste flux to the pads. If paste flux had been applied in the video, he wouldn't have had to go back and "fix" the solder fillets like he did. Roderick was depending on the residual flux from the solder to still be active enough to provide good fillets. Since the amount of solder was small, and the residual flux even smaller, the remaining flux will not always be enough to give you good solder fillets.

The flux provides an important function. It keeps the oxides from being created (or rapidly burns them off) so that the surface tension of the molten solder pulls the solder into as small an area as is possible. Without the flux, the oxides (which are created rapidly) greatly interfer with the pull of the solder, so you get solder peaks and cold joints. This will become an issue when you are soldering some fine pitch ICs and such.

Applying the flux is an extra step, and the residue is so messy that the board will have to be cleaned after you're done, but it is a worthwhile extra step to take.

 

Not quite... Between the application of the solder and the placement of the parts, you should ALWAYS apply paste flux to the pads.

Uh, oh! I completely forgot that extra step, you're right. In my case it's very important to have a very sticky component soldered on the board.

Applying the flux is an extra step, and the residue is so messy that the board will have to be cleaned after you're done, but it is a worthwhile extra step to take.

What you think about the "no clean" or "water washable" flux paste (e.g. the ones from Chipquick in syringe)?

 

What you think about the "no clean" or "water washable" flux paste (e.g. the ones from Chipquick in syringe)?

In a manufacturing environment, then maybe, but in a hand solder situation, the soldering is less controlled, so having the flux "outlast" the soldering operation is a definite plus. My experience has been in product development and prototyping environments. I found that cleaning with isopropyl alcohol and a stiff brush usually did the trick nicely.