Steve
By coincidence, I wrote an instruction manual for a new cleaning machine over the past
week. I finished it this morning. I quote from it:
"The most popular alloys, with a composition of tin, copper and silver, have melting
points about 40°C higher than the traditional tin/lead alloys. Although many fluxes
will be suitable with both alloys, it is to be expected that they will be much more
difficult to clean off when used at the higher temperatures.".
Now I know some paste/flux manufacturers deny this but - from LO-O-O-ONG experience, I
know that even 5°C can make some difference with both liquid fluxes and pastes, let
alone tens of degrees. The problem is that some of the flux/paste manufacturers, as a
rule, don't give at least one hoot, let alone two, about what happens to the residues
when you try to remove them, "Your cleaning process needs optimising" is about as much
as they say. In particular, you are using a rosin flux and rosin becomes mighty hard
when you insist with the calories.
Sorry if I sound cynical, to start the New Year, but I've had the doubtful pleasure of
all these problems for decades.
And I bet your boards had a high ionic contamination level after you spread the
residues around with your IPA and brush :-(
BTW, I'm not surprised either that ramping up the preheat produced worse results. You
should have tried that with a "no-clean" paste: you probably would not need to clean
the board afterwards because all the flux activators would have acted as VOCs long
before the board entered the fusion zone :-) Of course, the soldering results would
have been even worse, but that's neither here nor there if you want a clean board -- or
is there some bad logic here?
Brian
"Stephen R. Gregory" wrote:
> Hi Ya'll,
>
> Haven't chatted with ya'll since last year! (Yuk,yuk,yuk!) Hope you had a
> good holiday! Me, I stayed home for new years eve...wasn't even able to stay
> awake 'till midnight. Got woke up though from somebody in the apartments I
> stay at cutting loose with some sorta' automatic weapon at midnight...IDIOTS!
> Discretion being the better part of valor, I wasn't about to go tell some
> drunk okie not to be firing his gun in the air. I may do some dumb things
> once inna while, but I ain't STOOPID! (Hehehe..)
>
> Anyways, I've been playing around with some SN96AG04 solderpaste on some
> dummy boards and components trying to dial a good profile in. I took all your
> inputs when I asked about this before to help get me started. I called and
> got a few profiles from a few different paste vendors as well. I've got a
> Conceptronics HVA-70 (the little one, 10-zones, 5-upper, 5-lower)
>
> First thing I learned was that if I raised the preheat and soak temperatures
> too much higher than I normally do for a SN63 solder, I exhausted all my flux
> activity before all the paste liquified and coalesced into a fillet. I
> wound-up with a fillet that was covered with little teeny-tiny solder
> balls...almost looked like it was cold solder the balls were that small.
>
> So then I lowered everything back down in the preheat and soak regions and
> spiked the crap outta it in the last zones and things started looking better.
> My set points were:
>
> ZONE 1 ZONE 2 ZONE 3 ZONE 4 ZONE 5
> 140 150 160 175 300
> 140 150 160 175 300
> ZONE 6 ZONE 7 ZONE 8 ZONE 9 ZONE 10 Belt speed: 25 ipm
>
> I plotted it with my M.O.L.E. and was peaking out anywhere from 240-248º C.
> My ramp rates were all under 2º C per second till I got to the spike zone and
> then they went up around 2.4 - 2.8º C per second....one thermocouple at a
> sparsely populated area went up to 3.4º C per second. The joints looked
> better than my first stab...
>
> But I then tried to clean the flux residues (it was RMA), I put the board in
> our MCS-1000 (We run Kyzen Aquanox XJN at a 30% concentration) and the
> residues looked like they weren't touched...some got kinda' cloudy looking,
> but they stayed on the board. I couldn't get them off unless I took an acid
> brush and alcohol to the board. Is this normal? It was like the flux residues
> were polymerized from the heat?
>
> The paste I was using was out of date (that was all I could find to play
> with) maybe that has something to do with it...speaking of which, does
> anybody know where I can get some fresh SN96AG04 paste quickly? Every place
> I've tried says three-week lead time, and I gotta buy at least 10-jars.
>
> TIA,
>
> -Steve Gregory-
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
> the body:
> To subscribe: SUBSCRIBE TECHNET <your full name>
> To unsubscribe: SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> information.
> If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
> 847-509-9700 ext.5365
> ##############################################################
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################
|
