Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


double printing

Views: 1870

#48507

double printing | 20 March, 2007

Is there any down side, besides time, in printing the same board in both directions?

bill

reply »

#48512

double printing | 20 March, 2007

Print styles: Print - Most common print mode * A single print stroke forward on first board * A single print stroke reverse on next board Print-Print (Double Print) * Both forward and reverse printing strokes * Helps to ensure complete filling of the aperture * Possible bleeding of paste if the squeegee pressure is too high, or the gap too large Flood-Print * Forward stroke floods the stencil with paste * Accomplished by changes in pressure and/or down-stop of squeegee * �Flood Blades� * Rarely used for solder paste printing * Used mainly for hybrid applications Print-Flood * Reverse printing stroke followed by a forward flooding stroke * Rarely used for solder paste printing

reply »

#48522

double printing | 20 March, 2007

Hi Bill,

Gasketing between the board and stencil may leak alittle, giving you a fuzzy print. If not, you should be OK. Another variable may be you need to perform an understencil wipe more often, adding to your cycle time.

So why ya wanna double print?

reply »

#48546

double printing | 21 March, 2007

I wish you wouldn't have asked why! We had a rush job and the stencil maker used a frame (normally we don't use the frame type) and placed in the frame wrong so in order to get it to work we printed in both direction. So I thought maybe we should do this all the time

I'm 1500 miles away from the smt line and have a hard time getting people to pay attention to what they are doing.

reply »


IIT

#48552

double printing | 21 March, 2007

The biggest problem with double printing is that if the squeegee pressure and speed are correct, the stencil apertures are already filled with paste. Printing again can force paste between the bottom of the stencil and the top of the board creating a greater potential for bridging and solder balling.

reply »

#48554

double printing | 21 March, 2007

If you MUST double print, probably to get good aperture fill near board edges, I would recommend letting off on pressure (maybe 20%) to minimize the bleed. Alot depends on your board (gasket) quality.

reply »

PCB X-Ray Inspection

Plasma Prior to Conformal Coating