Dear Mr.Ricky,
        I have only a little experience to shear the idea with you.
        Your problem state on
        - Convex solder fillet on the IC lead.
        - Grainy on the solder joint.
        - Solder does not form a complete fillet on the pad.

        There are a few guidelines to verify.
        1. The oxidation or incomplete plating on the IC lead, it can interrupt
the solder flowing.
        2. Type of IC lead, the solder paste's recommended reflow spec is only the
guideline for manufacturing. Actually, different type of IC or PCB it need
the different reflow profile. For examples;
             2.1 Copper lead : require max temp at 210-220 degreeC.
             2.2  Alloy42 lead : require max temp at 225-230 degreeC.
             2.3 FR4 PCB with Tin/Lead plating : require time above melting point
= 30-60 sec.
                     2.4 FR4 PCB with gold plating : require time above
melting point = 45-75 sec.
              etc. For your getting idea only, there are a lot of factor such as
gold plate thickness, thin gold plating require max temp lower than thick
gold plating.
        3. Check your TC wire fixing. The size of TC wire coating is important and
sensitive to temp change especially the small joint such as the IC's. If
possible your profile board should be calibrated, 0 degreeC and 100 degreeC
by use the calibrated temp meter and the reading should not has a
plus/minus 5 degreeC tolerance.
        4. Oxidation or contamination on the pad. If your problem state on the
second side assembly only, your gold plating may be the soft gold that its
property has light change after pass some high heat, I don't know what is
it but I call it is gold oxidation.

        I hope above message can give you some idea to solve you problem.

With best regards,
Noppadol S.

At 15:23 3/6/98 +0000, you wrote:
> Hello everyone !
>
>We are experiencing here some solder quality problem after our solder
>reflow process. The quality of the solderability of components
>spcecifically the QFP IC's was not that good. The formation of the
>solder fillet was convex on the IC leads which sometimes looks to be
>grainy and sometimes it looks to be that the solder paste has
>suddenly stop from flowing to its desired area. We already checked
>the profile parameters of our reflow process and it is within the
>specs limit of the solder paste that we are using. Do you think that
>the thawing time of the solder paste have something to do with this
>kind of problem ? Thank you in advance to anyone that could give a
>solution to this problem.
>
>Regards,
>Ricky
>Electronics Assemblies, Inc. Phils.
>
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