Tombstones

I'm currently running a double sided paste smt board loaded with 0603's, on the secondary side. Many of the 0603 devices tombstone during reflow if the parts are not perfectly centered on the pads. Is this caused by the .008 foil thickness? Has anyone tried home plate type apertures for reducing tombstones? How about a .006 foil? I would appreciate any thoughts and comments. Thanks...........Ron

reply »

| I'm currently running a double sided paste smt board loaded with 0603's, on the secondary side. Many of the 0603 devices tombstone during reflow if the parts are not perfectly centered on the pads. Is this caused by the .008 foil thickness? Has anyone tried home plate type apertures for reducing tombstones? How about a .006 foil? | I would appreciate any thoughts and comments. | Thanks...........Ron Ron, We had run lot of 0603 package and never have problem with tombstone at all. here are some parameters that you could check stencil thickness should 6 or 7 mil , Placement accuracy,change the cooling fan at reflow oven to either low or medium and finally check the fab design to see if there are no groundplane on one side of the pad because groundplane take more heat than the non groundplane. Hope this help!!! Rin

reply »

Tombstoning is often caused by non-uniform heating. I suggest you check you profile to ensure you still have uniform heating and also check your rise and cool rates. If you have a convection oven I would look into the fan speeds or airflow rate through the process cavity to ensure you are not blowing the devices off the board. Another thing that caught my eye was that you said these parts are located on the secondary side. By this do you mean the Bottom side of the board? And if so are you conveying on an edge rail conveyor? Are you sure that they are not falling off the pad on one side because there is less surface tension when misaligned? Most commonly though I think this is related to non-uniform heating or cooling.

reply »

| I'm currently running a double sided paste smt board loaded with 0603's, on the secondary side. Many of the 0603 devices tombstone during reflow if the parts are not perfectly centered on the pads. Is this caused by the .008 foil thickness? Has anyone tried home plate type apertures for reducing tombstones? How about a .006 foil? | I would appreciate any thoughts and comments. | Thanks...........Ron We also run double sided paste and reflow boards with 0603 components on both sides. Along with placement accuracy and uniform heating being a key issues the printing process must also be in control. To address your questions, we are using a 6mil foil, home plate design, and electropolished stencils. Because of company policy I can't tell you your PPM defects, but I can say it is quite low. I would purchase one stencil with these parameters and perform a D.O.E. to determine the affect on your process. Good luck.

reply »