There you are, you're finally coming out with some concrete
information. To answer your questions, I am making a few
assumption.
First Q:
I don't think you can set a freq border where you leave the wave
solder pot all the time, or leave it on and off. This indecision is a
lot depend on your process req's, the condition of solder pot,
maintenance, and features of your wavesoldering machine.
One option is to collect a certain number of boards to be waved
and wave them all at once after a few setup/check. This is a lot
better option then leaving the solder pot on or on/off. Only the
conveyor and preheaters are remained on.
Minor preventive maintenance (removing dross, checking flux
concentration) should be performed every shift usually prior to
running boards thru the machine.
Major maintenance such as removing/cleaning/reassembling of
front/back plates, nozzle assy, pump and vane of solderpot and a
chemical analysis of solder should be performed monthly or 3
months or 6 months etc depending upon the freq of solderpot
usage.
A few indication of poorly maintained pot: freak-out noisy from
pump rotation, unsoldered joints, dirts on the bottom side of
boards, reduction of a flow solder height (cracking up the pump
to maintain a same height) and obvioiusly a heavy layer of dross
on the solder surface. Also if a freq adjustment of flow solder pot
indicate a large amount of dross formation.
All this shows the pump takes dross with molten solder thru flow
ducks and pump it out thru the nozzle. Therefore, the regular
removal of dross in the pot is a very important.
2nd Q:
Adjust your flow solder height so that it is a little bit higher than
the highest point of bottom side of board. This also depends on
how stable is the flowing solder and whether stiffeners are used
to keep boards from bowing down (remember Tg of FR4 is
about 130'c and pot temp is usally btw 240-260'c).
Sometimes, dirt on the top section of flowing solder are not
usually gets removed when the wave is turn on first time. This is
mainly because solder does not get flowed down smoothly thru
front and back plates. This can be usually fixed by adjusting
down front or back side plate or increasing the pump speed.
Run a dummy board prior to running a board. This allows you to
check the wave height, and remove dirt on the solder, and make
an initial push for a smooth solder flow.
From my experience, I didn't like to use the sensor on/off
function. The setting can be turned off from the machine
parameter setup (not by covering with a piece of tape). Usually
first board after the wave is turned on, gets screwed up and 2nd.
3rd... are excellent as long as it is not turned off and on again.
This is why in my opinion it is best to collect boards and run the
wave all at once (as per the First Q)
To be or Not be on. If on, creates too much dross, if on/off by
itself, first board gets screwed.
3rd Q:
You are asking one million dollar question here.
Yes, it is not unusal not to do touch-up after wave. This also
depends upon your process, solderbility of boards and
components, solderpot contamination and whatever... If you do 5
board touch-up out of 100, say I consider that's pretty good.
4th Q:
Flux should be dried prior to hitting the wave. If wet, it creates all
kinds of defects as per previous e-mail responses. It is just like
a frying a chicken wing in a oily bath. Can you image eating a ton
of fatty oil with the fried chicken? Ohh.. I hate that. Same thing
for greasy pizza's. Most flux mfg recommends 100'c to 120'c on
the component of board.
5th Q:
No excuses. You pick one typical board that go thru the wave a
lot, and perform the temp profile to check preheat temp's on the
component side of board. Adjust one variable at a time. Once it
is good, you keep that as the master profile. For other boards,
you adjust only one variable ( rec changing the conveyor speed
only) to get an acceptable result. Fix the solderpot temp at 250'c
or more/less and a board wetting time in the solderbath at 1 to 3
sec. I seldom change the wave profile unless it is big&heavy,
thicker board (0.092&up), thinner board (0.032) or too small.
6th Q:
It is outrageous. I totally and wholeheartedly agree with you.
Boards should only go thru wave once and should produce
acceptable result. You said boards supplied by your customer
are fluxed (instead of tin/lead finish). That reminds me of
rosin-based OSP that was used 20/30 years ago as a protective
coating from oxidation. I believe this is the sole responsibility of
your customer to supply you solderable boards.
For this board, try increasing a board wetting time in the solder
bath. It might work or might not.
7th Q:
Use nylon spacers to elevate LED's. Contact Bivar, mfg of nylon
spacers for electronic components. Tel: 714-951-8808, Fax:
714-951-3974 (it is in Irvine CA, USA)
Regards
Matthew Park
NII Norsat International Inc.
******
Now, to get to my main point, that's right, you are responsible for
getting this thing started. I got a few nasty, private and
confidential messages. Thanks for those people out there who
inflated and used political correctness from my technet
messages. The arrest and trial of production supervisor is in
order for the willful disobedience of process laws and tempering
machine settings. The place where I am, production mgr and
assembly people are too eager to pass a buck around and
ending up on my desk. Of couse, I meant process-related laws.
My guess was right, the responsibility of tackling this
wavesoldering problem is squarely up to you, Mr Chee.
>>> Hew How Chee <[log in to unmask]> February
20, 1998 9:44 pm >>>
Hello all again,
(for those who is just curious of who is who : the supervisor and
the
technician
, read the end of the mail)
I have read through the numerous responeses and will be
looking into
the problem very soon. But first, I'll be glad if anyone can provide
me
with more data.
1) From the feedbacks, some switched on the wave all the time
during
the wave soldering process and some mentioned the sensor is
there to be
used.
Can anyone provide me the typical frequency between boards
(going over
the solder wave) and turning the wave on all the time and also
the
frequency when intermittent wave should be used. On my side,
the
frequency is about 3-5 boards per minute.
What is the maintenance frequency of the wave solder machine
also ?.
2) It is known also that the (at my place) boards coming out from
the
wave machine
can sometimes have the corner sides not soldered (the rest is
OK). This
I belief is due to wave height and conveyor height. Comments ?
(The wave
is always on). Did
anybody face problem with wave height if the wave is switched
on and off
?
3) People tell me also that manual solder touch up is necessary
after
wave soldering.
What is the typical percentage of acceptable boards (no need
manual
touch up) after
going wave soldering ?. I want to check whether we are doing
too many
touch ups.
4) As for the flux, I'll be checking with the supplier. If I
remembered
correctly,
they called it SP-42. Ring any bells ?. Whether the flux should be
dry
or wet when
the board reaches the wave, most of the responses favours
dried flux.
(At my place,
I am having wet flux when the board reaches the wave, this might
explain
why quite a number of the boards have blowholes).
As for the preheat and flux activation temperature, contacting the
supplier should
solve the problem.
5) Determining the temperature profile for each board might not
be the
solution for us,maybe it is possible to have a general preheat
settings
or some formulas to
relate the preheat setting with the conveyor speed and PCB
profile?.
Over at my side, there is only one wave solder machine and I
suspose
that you need the wave machine to get the temperature profile ,
this
would sacrifice productivity.
6) My production supervisor also encountered PCB boards
supplied by
customer
that had to go through the wave machine twice. On the first time
pass,
insufficient solder resulted. On the second time, soldering is
much more
acceptable. The PCB is not tinned but are fluxed. I felt it is
ridiculous for a PCB to go through the wave machine twice. This
might be
due to the preheat temperature that is set too low.
(95-100 degree C). Any comments ? The diameter of the pads
on the board
might be
too big compared to the hole diameter. (I read something
relating the
pad size
and acceptability of soldering. IPC standards also, I think, has
recommendedations
for pad to hole size ratio.). Or is it another "not enough heat for
flux
activation problem" ?
7) Has anyone face rejects (of LEDs) when 3mm round LED is
mounted
directly to the board (its body touching the PCB) and is wave
soldered.
I know that this violates the manufacturer's temperature rating
but is
thare anyway
to solder the LEDs beside manual soldering ? (even manual
soldering
might violate the
temperature specs.). There is no room on the leads for
heatsinking as
the body is touching the PCB.
Hope someone can help.
How Chee
Malaysia
Note : I will not be able to see all your mail from Mon to Fri since I
have Net acess
only on Sat.
Who is Who ??
=============
p.s. : For those who are curious who is who. The maintenance
technician
is not
under the production supervisor and all of us reports to the
Operational
Manager and
NO roses are given. Over here, we are treated equally.
I apologized to all since I started this but I did get some laugh out
of
it.
(some entertainment compared to the routine techical things).
>
> At 11:23 AM 2/14/98 +0800, you wrote:
> >Hello,
> >
> >Can anybody please help or advice.
> >
> >I am trying to settle a dispute between my company's
production
> >supervisor and the maintenance technician on the wave
soldering
> >machine.
> >
> >1) The maintenance technician insisted that the wave should
be switched
> >on and off between boards to prevent/lessen "damage" to the
wave
> >creation mechanism.
> >(The wave can be switched on and off automatically by a
sensor on the
> >conveyor). My production supervisor think otherwise. She
covered the
> >sensor so that the wave would not be off.(She says the
sensor can
> >miss a board) So, who is right ?
> >
> >2) My production supervisor sets the preheat to about 95
degree C so
> >that
> >the flux would not dry up when the PCB board reaches the
wave and to
> >increase
> >solderability.(but this created a lotof residue on the solder
> >bath,according to maintenance).
> >My maintenance technician says the temperature should be
about 120
> >degree C
> >so that it dry up the flux before the board reaches the wave.
The reason
> >is so that
> >not much residue is created. Who is right again ??
> >
> >Thanks in advance.
> >
> >How Chee
> >Malaysia
> >
>
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