Gregg,

At limit, if too thick, these silkscreen lines could push the stencil up and bother printing, which is kinda critical for these packages. As a result - tombstones.

There is nothing like a properly made assembly drawing that accompanies the documentation, the assembly people will see the part orientations there. Also, the zero orientation in the CAD shall be the orientation of the parts inside the carrying tape, in order to avoid turning them during programming of the insertion machines.

Regards,

Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] 
W | www.digico.cc

N'imprimer que si nécessaire - Print only if you must

-----Message d'origine-----
De : Temkin, Gregg [mailto:[log in to unmask]] 
Envoyé : May-19-10 6:49 PM
À : [log in to unmask]
Objet : [TN] Component legend marking on PWB with 0402 components

On a first shipment from a new PWB supplier, we found all the 0402 component outlines deleted from our legend layers.  The PWB vendor said they automatically deleted the marking during DFM because it exceeded their manufacturing allowances and could have resulted in ink covering a portion of the pad.

Our in house PWB designer uses a program to develop his pad and marking dimensions.  The program would not generate a marking outline for this device, so he designed the outline to be the courtyard plus some manufacturing allowance.

Other vendors have supplied with PWBs with the same outline marking configuration; seemingly without any problem.

I've reviewed IPC-7351A, but couldn't find mention of PWB marking recommendations.  Is there guidance that I missed of is there another document I should be looking at?  Is it generally assumed that outline marking of 0402 and smaller devices is impractical?  Is placing a remotely located legend the best way of showing 0402 placement and orientation?

Thanks for your help.

Gregg




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