Also noted on previous fixtures, it's best if this "chimney" is chamfered to 
allow the solder better access.  Ability to do this does, however, depend on 
the proximity of adjacent components.

Jim Ennis
[log in to unmask]
 ----------
From: TechNet-request
To: rahollan
Cc: TechNet
Subject: RE: Selective Wave Soldering
Date: Wednesday, June 05, 1996 11:52AM

Ron,

In response to the attached email:

We are currently in the design/prototype stage of a new product that
requires selective wave soldering.

On the solder side of the pwb there are many high profile devices. The
tallest being a 140 pin SMT conn (height off the pwb is 7.5mm)

I designed a masking fixture out of a composite material ECP plus 8"L X
8"W X 12mm thick.

Because of the tallest component, the solder side of the pwb is 8.9mm from
the wave. The fixture creates a type of chimney which the wave must travel
up.

Preheat didn't seem to be a problem with this fixture probably due to the
use of 2 forced convection preheat sections and the last section having IR
panels top and bottom.

There was no problem getting the solder to go up "the chimney" the problem
was the solder flowing out properly. Therefore there was bridging on the
leads closest to the exit end of the component.

Two changes were made to eliminate the bridging.

        1. The pwb and fixture were revised where possible to allow more
           clearance around the leads to be soldered.

        2. The use of an air knife on the wave soldering equipment
           eliminated bridging in all areas.

Based on these tests we purchased an Electrovert Econopak Plus for the
production of this new product.

Good Luck

Dan Shea
Sr. Mfg. Engineer
The Foxboro Co.
Foxboro, MA 02035
[log in to unmask]


 --- Begin Included Message ---

Date: Tue, 04 Jun 96 16:32:16 EST
From: "Hollandsworth, Ron" <[log in to unmask]>
To: [log in to unmask]
Subject: Selective Wave Soldering
Status:

     I have been investigating selective wave soldering.  Results
     to date have been less than desirable.  The fixture is a
     huge heat sink, non-metal.  The objective is to keep my SMD
     away from the wave while soldering a few through hole parts
     and eliminate my glue operation.  The first fixture I tried
     held the CCA very high making it difficult to get successful
     soldering.  Current machines are two super modified, nitro
     burning Hollis GBS Marks that have been modified with a High
     Mass Preheats, and modified Hot Air Knives with very flat
     CFM response curves.  Also utilizing chip waves.  I would
     appreciate any and all recommendations or experiences you
     would be willing to share.  Thanks in advance.  Ron From
     Hollis Land.


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