Hello Elizabeth: There are lots of things to investigate to get to the
bottom of this issue.

1. Board design. Orientation of component relative to the direction of
travel over the solder pot.
2. Solder contamination. Contaminated solder will have a lower viscosity
than new solder and it could be the sluggishness which prevents it from
peeling off the bottom of the board.
3. Incline of the conveyor. The conveyor should be incline 5 to 6 degrees to
help the solder peel off the bottom of the board.
4. Uncured solder mask could also be a problem. Check the hardness of the
mask at soldering temperatures.
5. The no clean flux is not providing enough flux to help the solder peel
off the bottom of the board. For experimental purpose try a different type
of flux, perhaps something with a higher solid content.
6. Check the speed of the conveyor. You should be in the solder
approximately 1 to 2.3 seconds to get acceptable soldering.
7. Check to see if the board warps going over the wave. This will cause the
board to run deeper in the wave thereby changing the effective conveyor
speed, and it will impact the way the solder peels off the bottom side of
the board.

If you want to talk about this, please give me a call. 1 800 64 EPTAC

Good Luck
Leo Lambert
Technical Director
EPTAC Corp.

Check out our Web page at www.eptac.com

At 07:36 AM 4/23/97 -0400, Elizabeth Falk wrote:
>Dear Technet,
>I have a customer who is reporting bridging on the solder side of the board
>after wave soldering.  I have seen the boards, and they look quite messy,
>with solder sticking to the mask as well as between component leads and
>pads.  The mask itself is adhering nicely.  The mask is PC501 from Haven,
>with C101 hardener.  This was recently discontinued by MacDermid and picked
>up by Haven.  The flux is no clean, ENFLUX NCF-8660, and is under pressure
>with nitrogen.  The wave itself is at 500 degrees F, with preheats set to
>get the board to 210 to 220 degrees F when it hits the wave.  The same
>design board with LPI ran fine, so I do not suspect a problem in another
>area of the process.
>
>No other customers are reporting this problem, and I am at a loss as to
>where to investigate further. The customer is not happy, and wants a
>resolution today!  If anyone has any insights, please let me know.
>
>Thanks,
>Elizabeth Falk
>Process Engineer, Beaverbrook Circuits
>
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