Homebrew PCBs

Hi guys,

After lots of "umm"-ing and "aah"-ing, I've decided to take the plunge 
and have a go at SMD reflow using a toaster oven (or, in my case, a 
"mini oven").

I spent about 3 days digging through all the articles I could find on 
the subject, and eventually found an article in Elektor (November 2008 
if memory serves) that included a short list of features that are 
required in an oven that is being modified for SMD reflow:
   - Must be able to reach 250 degrees Celsius
   - Heater power of around 1500 Watts

Turns out there was only oven in the current Argos catalogue that met 
these specs -- sold under the brand "Cookworks", part number MG25AF, 
Argos catalogue number 423/0302. The features of this particular oven 
are as follows:
   - Four elements (two top, two bottom), 1640W total.
   - 25 litre oven capacity
   - Timer up to 120 minutes
   - Thermostat settings from <70 to 250C
   - Can switch the elements on and off via a front-panel switch. Either 
all on, top only, bottom only or all off.

I haven't had chance to etch a PCB and solder it (yet), but I did put a 
thermocouple in there tonight, set the timer to the full 2 hours (but 
only ran it for about 20 minutes total), all elements on, and full heat 
(250 Celsius). The sensor was a Labfacility Z3, fibreglass-sheathed, 
connected to a Maxim MAX6675 K-type thermocouple interface IC 
("thermocouple to digital converter" according to the datasheet).

I could upload the CSV file containing the captured data, and the 
OpenOffice (ODS) spreadsheet file containing said data, nicely graphed. 
It covers the time from switching the oven on, to it oven heating up to 
~300C (despite being set to 250C), the oven being switched off, and then 
the oven cooling down to ~50C with the door closed.

Thanks,
-- 
Phil.
ygroups@...
http://www.philpem.me.uk/

Hi Phil


some time ago I visited a large SMD assembly house, 
and I remember the guy touring us  mentioning that the ovens   
( quite a few 3 metters long ) were the card is soldered when
 traveling inside it, has a totally controlled, very sharp and 
fast heating and latter cooling, that should follow some rigid 
temperature curves in order to preserve the components.

I am looking for this information before deciding to go on on the project.

regards

jjose

"juanabba" <jjose.2008@...> writes:
> I am looking for this information before deciding to go on on the project.

Most SMD parts have the reflow profiles in their data sheets.  When
reflowing a board, you have to find a profile that meets the profile
specs of all the parts.

I don't think sharp and fast heating are the correct terms. It is
rather more gradual with preheat to give moisture the chance to gas
out and stuff. The profiles can be found easily, but apart from a
restriction on how long you should stay over a certain temperature
(longer and the solder may start to dissolve the metallized film
terminations on chip components) there is usually a restriction given
how _slow_ you have to increase the heat.

ST

On Tue, Aug 18, 2009 at 12:11 AM, juanabba<jjose.2008@...> wrote:
> Hi Phil
>
>
> some time ago I visited a large SMD assembly house,
> and I remember the guy touring us  mentioning that the ovens
> ( quite a few 3 metters long ) were the card is soldered when
>  traveling inside it, has a totally controlled, very sharp and
> fast heating and latter cooling, that should follow some rigid
> temperature curves in order to preserve the components.
>
> I am looking for this information before deciding to go on on the project.
>
> regards
>
> jjose
>
>
>
>

>> some time ago I visited a large SMD assembly house,
>> and I remember the guy touring us  mentioning that the ovens
>> ( quite a few 3 metters long ) were the card is soldered when
>>  traveling inside it, has a totally controlled, very sharp and
>> fast heating and latter cooling, that should follow some rigid
>> temperature curves in order to preserve the components.
>>
>> I am looking for this information before deciding to go on on the 
>> project.
>>
>> regards
>>
>> jjose


Hi Jjose

Have a look @ the "tech reflow controller" from Silicon Horizon

http://www.thesiliconhorizon.com/images/techFXreflow.pdf

I'm using it for 2 years now with a small low cost "quartz oven" (20 bucks 
at Target) . It's probably the best price/performance ratio I've seen, 
better than the Elektor one (As I own those two babes in my shack)

The heating curve is fully tunable, and you can even use this system to 
"dry" large IC's before soldering (heating cycle @ 90\ufffdCelsisus during 24H). 
With a computer driving the gear via USB cable, you can manage as many 
temperature curves as you want. You only need to be able to create Excel -or 
OpenOffice speadsheet- files that define the time/temperature params.

After building a reflow oven, the next step is to find a solder dispenser 
(on ebay for eg.)... :-)

As far as I know, many ham radio in the UK have adopted this technique (and 
this very same process control item). You'll probably be able to find some 
of them on the forum section of Silicon Horizon's web server


Regards
Marc