Krishnan,
Thank you very much for sharing this information! This is exactly what I
have been experiencing. I would also like to thank everyone for their
responses, they have all been helpful. I have been able take photos that
relate the solder balls to the mask eruptions and have emailed them to the
supplier to eliminate the root cause, while we IR reflow the boards at our
end.
Thank you,
Paul Black
Manufacturing Engineer
Kronos
-----Original Message-----
From: Chezhian, Krishnan [mailto:[log in to unmask]]
Sent: Thursday, September 25, 2003 1:23 AM
To: [log in to unmask]
Subject: Re: [TN] Solder Balls
Hi Paul,
This is a common problem in the industry when the customer asks for the via
holes to be plugged with soldermask & if the PBW fabricator does not do a
good job of plugging the holes you will end with solder balls. Basically
when plugging is done it is done from one side either component side or
solder side depending on the board design, fine pitch devices, closely
spaced features etc., would end up having soldermask smear after the
plugging process, hence it would be plugged from the non-critical side. When
the vias are not plugged sufficiently (%hole fill), solder from the
subsequent HASL process wold get entrapped inside these vias which are
attached to the plugged soldermask inside the vias & may not be visible to
the naked eye, these solder balls would then pop-out during the IR reflow
process at the assembly side, those that are visible would be entrapped
inside but attached to the hole wall copper & would not pop-out during the
IR reflow process at the assembly side.
Normally you would see that when the plugging is done from the component
side & top-side is being reflowed the solder balls will pop-out on the
solder side or bottom side making it difficult to print solder paste on the
bottom-side. The only way out here is increase the %hole fill by the
fabricator to ensure no solder entrapment & for those boards that have been
already fabricated & in WIP to send them through the IR reflow as bare
boards to pop-out the solder balls & take a plastic paper cutter or
non-metallic knife & run it across the board to remove the popped out solder
balls & then your assembly would not have any problems. Baking the boards
will not help as you need temperature & gravity for the solder ball to pop
out & make sure you place the boards with the plugging side facing top
during the IR reflow process.
Hope this helps.
Thanks,
Krishnan
-----Original Message-----
From: Reuven ROKAH [mailto:[log in to unmask]]
Sent: Thursday, September 25, 2003 1:08 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Balls
Hello Paul,
The reason is : Vial holes, plugged by solder that come from the HASL
process.
You have to instruct the PCBs fab to increase the air pressure during the
HASL.
Other reason is, when you have plugging via holes requirement and the HASL
process is done after the plugging process and not before.
Best Regards
ROKAH Reuven
Chief Engineer
ECI Telecom LTD.
Operations Division
30 Hasivim St. Petah-Tikva 49517
ISRAEL
Tel: 972-3-9266734 Mobile:972-55-786734
Fax: 972-3-9266480
e mail: [log in to unmask]
"Black, Paul"
<[log in to unmask] To: [log in to unmask]
OM> cc:
Sent by: TechNet Subject: [TN] Solder Balls
<[log in to unmask]
>
24/09/2003 14:57
Please respond
to "TechNet
E-Mail Forum.";
Please respond
to "Black, Paul"
Hi TechNet Gurus,
Has anyone experienced solder balls resulting from the board fabrication
process? We have been getting them from our offshore supplier for a few
months now and have had to add a wash step to our no-clean process. We know
that it's fro the board because we have run bare boards through the reflow
oven using the normal reflow recipe from that board and we are seeing 25-60
random solder balls on our 9" x 7", 8 layer, .062", HASL FR4 board. We
believe the problem is caused by uncured solder mask that erupts when
exposed to reflow temperatures but have been unsuccessful trying to
eliminate the problem. We have tried baking the board @ 320 F for anywhere
from 1.5 - 6 hours. This has reduced the number of solder balls to maybe a
dozen or less. Anyone have a suggestion?
Thank you,
Paul Black
Manufacturing Engineer
Kronos
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