On Thu, Mar 26, 2009 at 5:08 PM, Joseph Bento <joseph@kirtland.com> wrote:
>
> Yes. =A0Even a toaster oven can be made to work for SMT soldering. =A0A
> convection oven with internal fan is preferable for better heat
> distribution. While a hotplate will work, most boards I've encountered
> are not perfectly flat, thereby greatly affecting the heat transfer.

* I heard that oil helps to evenly disperse heat. Also, some dude put
an aluminum block on his pan to distribute heat from the element.

* Also, do you recommend closed ovens or open type frying pans/skillets/etc?

> Yes, heat damages components. =A0It's the way the heat is applied,
> however. =A0A solder iron may have a tip temperature of over 400c. =A0At
> this temperature, you need to complete your connection quickly or else
> rish damaging the component. =A0If you use an oven with paste solder for
> SMT components, you will typically limit the temperature to around
> 200c. =A0Paste solder turns liquid at around 170c. =A0 I have hand
> assembled many boards with SMT components and have never seen a
> component damaged in a 200c oven.

Thanks. I'll try and make something using my old oven that hasn't been
used in 10 years. It's really solid (but old), heats up quick and very
hot.

> We used this method with .4mm pitch chips and resistors as small as
> 0402. =A0It works surprisingly well, and for a small shop that can't
> afford SMD ovens, it is perfectly adequate.

This is heartwarming to know. I just might buy all surface mount
components from now on since the soldering part should be easy and I
already asked a million questions about making PCBs, so that should be
good too.

> If you're hand soldering the components, don't worry. =A0It is exactly
> because of trapped moisture that can otherwise affect the quality of
> the soldering. =A0When flowed, it is possible for the joint to
> crystalize if the moisture content is too high.

If the components I purchased/sampled did NOT come with a flashy
sticker telling me to pre-cook the chip before reflow soldering, do I
HAVE to cook it or can I go straight to the reflow soldering? I think
my parents would kill me if I left an oven on for 24 hours...

> If you are placing SMD parts by hand, the solder is applied via a
> blunt hypodermic needle. =A0There are several sizes depending on the
> pitch of component you are working with, affecting the flow out of the
> needle. =A0Typically, the dispenser is the paste solder, and the needle
> screws right on the end. =A0There is a air operated foot pedal to
> pressurize the dispenser, allowing the solder to flow.
>
> It can be done with a plunger applicator as well. =A0When doing an IC,
> it is not necessary to exactly apply the paste to each pad. =A0You can
> draw a small bead across the length of the pads, place the chip, and
> through practice, you will slide your soldering iron across the pads
> and perfectly soldering your component. =A0You can also use a hot air
> machine if you have access to one.

Is the solder paste really toxic? I think it should be ok if I use
some medical-purpose gloves, no?

> It really does work. =A0Applying the paste and a steady hand with
> tweezers to place the parts may be the most difficult step.

All in all, do you (to everyone) recommend reflow soldering or normal
hand soldering? Is homebrew reflow soldering worthwhile, in your
opinion?

And solder paste seems to be expensive...

-- =

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