The answer is - it depends - on the circuit board base finish.
For example gold finish enig boards will "obviously" show where solder has
wetted to the board.
On the other Hand silver immersion boards are silver to start with, and
solder is very mobile on a silver finish. When you reflow the board all of
the available solder is drawn into the joint area due to this mobility and
can result in a pad that looks "dewetted" when in fact all that has happened
is that the solder is actually in the joint area - where it is required.
It is important to understand this effect particularly where the pads are
"too long" to avoid rejecting perfectly good joints.
I first came upon this effect about 10 years ago, and went through a lot of
trouble with wetting balance testing on reflowed and non reflowed pads to
understand what was occurring.
If indeed you are using silver and you say your wetting angles are good a
simple test should prove the point - take a soldering iron and apply it and
solder to the "dewetted" pad - did the solder take to the joint areas?
John Burke
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Thursday, September 17, 2009 7:45 AM
To: [log in to unmask]
Subject: [TN] IPC-610 vs lab results
Dear Technos,
I have to get out of this situation regarding the quality of certain boards:
· On one hand certain pads have the visual aspect of dewetting,
being, once again, visually just like in Figure 5-41 para 5.2.5 of IPC-610
· On the other hand I have 2 lab reports, reputed labs, saying the
joints are reliable (good wetting angles and IMC)
The visual confusion comes from the excessive length of the pads, the solder
kinda fades away before reaching the tip of the pads, but everything looks
very well in the component pin area.
The question is: is there any IPC document stating something like "IPC-610
is a visual guide only, lab results overrule it"? Otherwise said, the joint
quality is there, proved by x-sectioning, so why bother with the visual
aspect.
Thanks,
Ioan Tempea, ing.
Ingénieur Principal Fabrication / Sr. Manufacturing Engineer
30 ans déjà! - 30 years already!
950 rue Bergar, Laval, Québec, H7L 5A1
t : 450-967-7100 ext : 244
Mtl : 514-990-5762
f : 450-967-7444
[log in to unmask] <mailto:[log in to unmask]>
www.digico.cc <http://www.digico.cc/>
P N'imprimer que si nécessaire - Print only if you must
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