SMT SOLDERING PROBLEMS

In some of SMT PCBs, we get black coloured dull finish /soldering joints on leads for QFP. What is the reason for getting this black colour finish . If we use the same IC on some other board for the same pitch location ,we get good soldering result. What is the reason for this. We have identified one problem in the PCB for that IC ( QFP) , ie the IC land area is not suitable ( area is less) for the IC. If we change the pad/ land area size, will the problem get solved.Please advise.

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