Recipe for a soufflé omelette.
Take 3 eggs separate the whites, beat whites until fluffy, add yolks, mix
briefly into fluffed whites, pour into a hot pan coated with butter for 30
to 60 seconds. Place under broiler to allow top to seal and then the
omellette will naturally rise - do not over cook the top, but rather
transfer back to hot plate to cook to taste.
Recipe for SMT
Paste, check, place components within 10 minutes, reflow within 10 minutes
after that..........8-)
Don't ask "how long can it remain there" but rather change the process to
minimize the time if you want perfect results.
John
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Friday, September 29, 2006 4:31 PM
To: [log in to unmask]
Subject: Re: [TN] Solder paste question
After printing the solder paste is vulnerable to cold slump as noted, also
the surface to volume ratio of the printed paste deposits is high so egress
of solvents and ingress of moisture is an issue resulting in loss of tack,
poor wetting and so on.
The actual times for these things to happen will vary according to paste
type , supplier formulations and environment.
IPC tests are conducted in standardised conditions which may not be
representative of actual factory floor conditions, they should theorem be
treated more as comparitive guides rather than absolute facts.
If you need to batch boards after printing before placing then you need a
constant temperature low humidity low draft environment. In an ideal world
you will have a nitrogen flushed cabinet to flat rack them in. . At the
other end of the scale you could just put them flat in Tupperware type
containers, maybe with a silica desiccant.
Regards
Mike Fenner
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
W: www.indium.com
Pb-free: www.Pb-Free.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Wednesday, September 27, 2006 9:26 PM
To: [log in to unmask]
Subject: Re: [TN] Solder paste question
A little bit of tack testing and plenty of information on slump test is
covered in J-STD-005 and J-STD-006, and in the TMs in 650 called out
within those documents, but probably not enough regarding the
application of the pastes.
The application is important as well, ie, if you are running a
high-speed turret-type placer the tackiness and slump qualities are much
more critical than if you are running a gantry style placer. And if you
are dealing with pitches of .8mm or less, again the ability of the paste
to form a good, clean brick without slumping is again very critical.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Wednesday, September 27, 2006 2:12 PM
To: [log in to unmask]
Subject: Re: [TN] Solder paste question
Thanks for the correction Steve. I have seen the equipment that
does the Sipad process and talked with one of the fellows that is
pioneering that process in the USA at length. The main point, some
pastes loose their tackiness in about an hour and some last as Steve
said much longer. A test should be made to see how long does a
particular formulation keeps its tackiness and then stay within the
time. Of course the test board should be fully inspected for good solder
joints.
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, September 27, 2006 2:16 PM
To: [log in to unmask]
Subject: Re: [TN] Solder paste question
Solder Pastes that are tacky for weeks? I don't think so.
SiPad is not a solder paste but a solid solder deposit that has been
flattened and then a tacky flux applied over that. Then the board is
covered with a slip sheet to keep the tacky flux reasonably fresh.
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Wednesday, September 27, 2006 1:00 PM
To: [log in to unmask]
Subject: Re: [TN] Solder paste question
Joel:
Some pastes can be tacky for weeks (Sipad) and some will loose
their tackiness in an hour and parts start sliding over the solder
balls, at which time parts need to be taken off the board, board cleaned
and part placement process started again. It all depends on the solder
paste formulation. Placing a board on its side will risk parts sliding
down, not recommended, unless you are using Sipad, very tacky firm
paste.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, September 27, 2006 11:27 AM
To: [log in to unmask]
Subject: Re: [TN] Solder paste question
Hi Joel!
First off, I'm not aware of any "Industry Standard", because it's all
going to depend on the solder paste. All solder paste "slumps" to one
degree or another, depending on the formulation, environment, etc..
Personally, I wouldn't like to see a printed board set for more than an
hour or two before it was placed if you can help it...especially if
there's any fine pitch or BGA's on the board.
Saying that, there's been some unusual circumstances where I've had to
hand place boards and they've sat for eight hours before I had all the
components placed and the boards reflowed. Once or twice in another
life, it's taken more than a day to finish hand placing a board (I don't
ever want to do that again!) and getting it in the oven. Did the boards
reflow okay? Kinda'...there WAS just a little touch-up needed! (GRIN)
When you say sideways on a tray, are you talking about tilt-racks?
Because if you are, I would say that isn't a good idea. Gravity is only
going to exacerbate any slump issues that the paste experiences.
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask] <mailto:[log in to unmask]> ] On
Behalf Of Joel Alexander
Sent: Wednesday, September 27, 2006 10:06 AM
To: [log in to unmask]
Subject: [TN] Solder paste question
Is there any industry standard on how long a printed board can sit prior
to reflow? Also if a printed board is placed sideways on a tray, can
this cause print quality issues?
Joel Alexander
APSCO Quality Assurance Manager
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