I suppose that the placement is not symmetrical. Check if the lifting is
always on the same diodes at the same lead. The general picture for
tombstoning shows a perpendicular position, but it is not a must. Check
if the lifted termination is solder wetted on the circuit. Melfs are
known to be problematic.
Gaby

Becerra Alejandro wrote:

>
>
> We have had problems with lifted components (Like tombstoning but the
> component is lifted just above the solder in one pad)
>
> The component is a MELF cylindrical diode.
> We made solderability test (Dip and look) and we did not found any
> differences between the terminals.
> We measured the component and we did not found differences between the
> diameter of the terminals.
> The component length is 3.4 mm and the diameter is 1.5 mm.
> I have pictures of the cross section of one defect but I could not
> attach them in the mail.
> Cross section shows that one terminal is "sink" in the solder causing
> a lifting in the other terminal.
> A 6 mil. stencil is used in this process.
>
>
>
>                           Alejandro Becerra
>
>               Phone (915) 841-8439, Fax (915) 841-8401
>
>                            [log in to unmask]
>