Soldering 402 chip R's

I just use an iron. You need to actively hold them down or they'll get sucked into the solder blob by surface tension. I tin one side, attach the resistor then resolder both sides to make it pretty. A bit slow, and you can expect to lose (as in never see again) some percentage of the part.

Best regards, Spehro Pefhany

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Sounds like you're rather skillful. I can hardly see these buggers with the naked eye. They're about the size of a grain of sand. So you remove them from the paper, place it on the PCB, then place an iron across the entire R? What percentage of R's will stick to the iron?

100.

No.

Get an illuminated magnifier or some 2.5x granny glasses.

Small-tip soldering iron.

Blob a little solder onto one pad.

Place resistor with tweezers, and reheat that pad to solder one side.

Solder the other side.

Touch up as required.

Practice.

Or design with huge parts, like 0805's.

John

Granny glasses is a good one :-)

The Weller ETS tip is my favorite. Keep super clean, use sponge often.

With the emphasis on "a little". Kester 15mil no-clean still looks like a sewer pipe compared to 0402 but it's the smallest I could find that worked.

I often use a tooth pick to hold them down.

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Regards, Joerg

http://www.analogconsultants.com

Why use the naked eye? I go up 5 diopters from my standard (nearsighted, thus negative) prescription. Means a max working distance of 20 cm, but it gets the job done. Add plenty of light, especially if your eyes are not those of a young whippersnapper. Use a microscope if that won't do it. Place the part, hold it down with tweezers (or some other means - I've been thinking about some sort of "flexible whisker clamp", or possibly a headstick), hit one end with the iron (add a touch of solder to the iron tip, or tin the pad a bit ahead of time). Now solder the other end properly, and come back around to solder the first end properly. Use teeny tiny wire solder - if you grab a mechanical pencil the same size as your solder, you can use the mechanical pencil as a solder feeder.

At the design phase, if you don't need to go tiny, don't. If you are prototyping something that will be built in mass quantities and you need to do one with the same scale components, fine; if you need the whole thing to be really tiny, even if you are only building one, fine; if you have no reason not to use 0805, then use 0805...you can put them together faster by hand.

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Lots of practice! I found a good deal on even small 201 case SMD R's. The application is high frequency up to 30 GHz, hence the need to small R's. Supposedly Thin films are best at such high frequencies as long as it's not a wrap around design.

I bought some solder paste. Absolute junk for this application. I thought perhaps someone could talk about soldering liquid. The idea is to dip a room temp need in the solder liquid, dab it on the R's pad, touch it with a hot solder tip needle. What do you think?

Solder paste. Either screen it on, or dab it from a syringe. Then place all your parts onto the paste. Then, you can reflow the parts many ways:

1. reflow oven

1. hotplate (my at-home choice, at Target)

2. heat the board near the part and let the heat flow to the solder (assuming you can) using an iron or hot air pencil

1. hold the part down with something (tweezers, toothpick; press down gently on the top) and touch the two ends with the iron.

The key is having the paste between the part and the board. That means one less thing to worry about, and one less thing to stick to the iron instead of the part. It also frees up a hand (the one that held the solder), so you have one to hold the part and one to hold the iron.

I use SynTECH paste from stencilsunlimited.com. Mine's been unrefrigerated for about a year now and still works just fine.

On Sep 19, 2:31 pm, DJ Delorie wrote: [snip]

That's true. I'm wondering how people are holding the R down with tweezers, holding the solder, and soldering iron all at once.

Good to hear someone's getting good results with the paste. I bought some last week. Hated it. Brand name Solder It. It was very grainy and lumpy. Each grain was probably the size of a 402 chip.

I'll see if the local store has the brand you mentioned. What do you think of the liquid solders? I thought the liquids would be better for 402 201 case R's.

On Sep 19, 2:07 pm, John Larkin wrote: [snip]

How about this -->

Hold tooth pick (or tweezer) with index finger and thumb of left hand, solder with ring and middle finger of left hand, solder iron with right hand. I've seen a guy additionally holding a cigarette in that right hand but that's a no-no in my lab. He had a separate sponge tray and the Weller sponge tray had become the ash tray ...

It helps a lot to have some training eating with chop sticks. Seriously. Or try to train the Spaceship Enterprise greeting.

[...]

--
Regards, Joerg

http://www.analogconsultants.com

Hold the solder in your teeth. ;-)

Cheers! Rich

An Optivisor

works well if you don't need large magnification. The 5 diopter (about 2.5x) has an 8" working distance so you're not nose to tip with the soldering iron... Various accessories available.

Beware of the cheap magnifiers with the cast acrylic lenses. You might get lucky but most of the time you just get a headache.

I have the OptiVISOR with both the 5 (2.5x) and 10 (3.5x) lenses. The

5 is my favorite for most work, including 0603 parts and 0.5mm pitch. For smaller parts, the 10 works fine, but it takes a few minutes for my eyes to adjust to "normal" vision afterwards.

Of course, now that I have it, I use it for lots of other things - scroll sawing, splinters, pcb drilling, etc.

What he said. I also like using a flux pen if the PCB doesn't wet instantly.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I think we all already told you how to do it.

John

I really like my Mantis:

That's, umm, not me in the picture.

John

You could also set up a macro camera (with plenty of light, but plenty of light is good with any of these methods) and a 19-22 inch monitor. I'll probably end up there one day - eyes don't improve with age. It would certainly help with the "Post 5 diopter vision adjustment period", and might offer a zoom option easily.

There are also various types of telescopic magnifiers for longer working distance, but they appear to give you a great deal of tunnel vision - which not a problem with "overly strong reading glasses", and they are a lot more expensive.

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Cats, coffee, chocolate...vices to live by