Richard Philp said:
> I am more familiar with test than board manufacture and would welcome
> an answer to a simple question. The quality of the connection depends
> on a number of characteristics of a reflow oven - pre-heat,
> temperature and time in the oven. CORRECT?
And many other factors, but the oven settings will have influence, yes.
> If so, is there something I can attach to boards as they go through
> the system to ensure that the settings are correct for the particular
> boards?
A MOLE (multichannel occurent logger evaluator) or equivalent is used, the
device passes through the furnace with the board, has thermocouples which
attach to various points on the board and logs the temperature with respect
to time. Software on a PC plots a time-temp graph which indicates peak temp
and the rate of increase, also shows the relative high and low temps across
the board surface. This is called "profiling". Vendors for this equipment
include ECD, KIC and DataPaq.
> I am thinking of a substance that changes characteristics,
> say colour, at a rate depending on the temperature.
Yes, and you could use a VOM to troubleshoot your digital logic, too. You
need a MOLE to do it right, and you should be familiar with the reasons for
and effects of profile changes.
> We manufacture
> small quantities but large variety and thus the settings are
> potentially needing changing regularly.
Most people use 2-3 different profiles, and vary the conveyor rate of the
furnace to handle different boards based on thermal mass, etc.
> I want to eliminate faults before I have to test. I would normally
> ask the in-house expert but he is taking a well earned rest.
Speaking as a process engineer, if I returned from vacation and one of the
test guys had changed my oven profiles in my absence, serious levels of
verbal abuse would be certain, and physical violence possible. I am usually
very energetic after a nice rest.
My suggestion is to call your flux supplier, and ask them if they could
assist in evaluating a profile. Most of them will have the necessary
equipment and experience to do this.
If you're desperate, and if you are the reckless type, try changing the
conveyor rate slightly (faster for lower peaks, slower for higher peaks) no
more than 5-10%, then look for changes in the wetting rate of the solder or
for discoloration of the laminate. When peaks are too high, the FR-4 may
turn brownish. If the peak is too low, you may see the highest thermal mass
parts not wetting.
> Thanks in advance.
>
> Richard Philp,
You bet.
Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com
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