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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Via in the middle of a pad

Michael Selva

#7999

Via in the middle of a pad | 4 January, 2000

One of the boards has a via designed right in the middle of a pad for a 1206 cap, one side only. This causes the solder paste to run into the via during reflow. We run No-Clean paste. One alternative is to increase the aperture on the stencil for that pad but that may create solder balls. Does somebody have other alternatives? Thank you

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#8000

Re: Via in the middle of a pad | 4 January, 2000

don't you just love those design guys sometimes, this is an issue that pops up every once in a while with us too. We have a couple assemblies that have hundreds of vias on pads. We have tried and had some sucess with: increasing squeegee pressure, actually screening the pcb twice to force paste into the via. The best way is to redesign but if you still have to build them you will probibly have some level of touch-up no matter what you do..

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Millerin

#8001

Re: Via in the middle of a pad | 5 January, 2000

Some PCB's manufacturers are now able to fill the hole and then re-metallized the pattern in order to obtain a final soldering surface perfectly flat but with an electrical connection under. This of course increase the price of the pcb but avoid any soldering troubles

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#8002

Re: Via in the middle of a pad | 5 January, 2000

Millerin: You are generally correct about plugging and over plating vias, but in Michaels case, the via is blind. Plugging would trap air between the bottom of the via and the plug material, causing an air pocket. When heated to soldering temperature, the trapped air will expand and could fire the plug across the room.

Ta

Dave F

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Istv�n Dominik

#8003

Re: Via in the middle of a pad | 10 January, 2000

We had the same problems. Certainly the best solution to redesign the boards. Otherwise the holes must be plugged. We tried many solutions (more paste, printing twice etc.) but the result was almost the same. Finally we printed solderpaste only on these pads and sent the bare board through the reflow oven. This way there were no holes on the pads. After that we applied the normal process and the solder joints were OK.

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TNT

#8004

Re: Via in the middle of a pad | 10 January, 2000

HELLO MIKE, THE PROBLEM WITH THE VIA BEING IN THE MIDDLE OF THE PAD CAN BE HANDLED. IF YOU ARE HAVING PROBLEMS WITH SOLDER FLOWING THROUGH AT REFLOW YOU MIGHT WANT TO CHECK YOUR VACUUM AT YOU SCREEN PRINTER. SOMETIMES THE VACUUM THAT HOLDS THE PCB DURING THE PRINTING PULLS THE PASTE INTO THE VIA. YOU CAN ALSO EPOXY THE COMPONENTS AT SMT THE ADD SOLDER AT THE WAVE SOLDER. I HOPE THIS HELPS.

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David

#8005

Re: Via in the middle of a pad | 11 January, 2000

Is this a thru hole via or a blind via? What is the hole diameter? If blind, how deep is it?

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