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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