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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


David Spilker

#16451

Film Capacitors - Tombstoning or Drawbridging Problems | 25 March, 1998

We are having some problems with "drawbridging" on 0805 film capacitors. We have already reduced the pad width from .050" to .040" based on input from vendor. Defects appear to be random as far as location on the PWB and direction of placement. We are considering going to a pad width of .035" or less. Is anyone running this type of part without any problems? Is pad size the real key? Is there a recommended pad size?

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Mcox

#16453

Re: Film Capacitors - Tombstoning or Drawbridging Problems | 25 March, 1998

| We are having some problems with "drawbridging" on 0805 film capacitors. | We have already reduced the pad width from .050" to .040" based on input | from vendor. Defects appear to be random as far as location on the PWB and direction | of placement. We are considering going to a pad width of .035" or less. Is anyone running | this type of part without any problems? Is pad size the real key? Is there a recommended pad | size? From my experience I have seen four possible scenario that can cause this 1) Component solderability (Find out what the plating is on the cap) 2) Uneven heating (one end becoming liquidous before the other sometimes caused by heavy traces or a poor reflow profile) 3) Component placement (to far to one end) 4) Pad layout(try reducing the pad dimension beyond the cap termination, reducing the end pad dimension will reduce the amount of surface tension) Lots of luck Mike

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Earl Moon

#16454

Re: Film Capacitors - Tombstoning or Drawbridging Problems | 25 March, 1998

| | We are having some problems with "drawbridging" on 0805 film capacitors. | | We have already reduced the pad width from .050" to .040" based on input | | from vendor. Defects appear to be random as far as location on the PWB and direction | | of placement. We are considering going to a pad width of .035" or less. Is anyone running | | this type of part without any problems? Is pad size the real key? Is there a recommended pad | | size? | From my experience I have seen four possible scenario that can cause this | 1) Component solderability (Find out what the plating is on the cap) | 2) Uneven heating (one end becoming liquidous before the other sometimes caused by heavy traces or a poor reflow profile) | 3) Component placement (to far to one end) | 4) Pad layout(try reducing the pad dimension beyond the cap termination, reducing the end pad dimension will reduce the amount of surface tension) | Lots of luck | Mike

Mike covered it all. The problem should not exist. You may have hit on one other thing as solderability of end termination area though non wetting will be clearly evident.

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Michael Fogel

#16455

Re: Film Capacitors - Tombstoning or Drawbridging Problems | 29 March, 1998

| | | We are having some problems with "drawbridging" on 0805 film capacitors. | | | We have already reduced the pad width from .050" to .040" based on input | | | from vendor. Defects appear to be random as far as location on the PWB and direction | | | of placement. We are considering going to a pad width of .035" or less. Is anyone running | | | this type of part without any problems? Is pad size the real key? Is there a recommended pad | | | size? | | From my experience I have seen four possible scenario that can cause this | | 1) Component solderability (Find out what the plating is on the cap) | | 2) Uneven heating (one end becoming liquidous before the other sometimes caused by heavy traces or a poor reflow profile) | | 3) Component placement (to far to one end) | | 4) Pad layout(try reducing the pad dimension beyond the cap termination, reducing the end pad dimension will reduce the amount of surface tension) | | Lots of luck | | Mike | | Mike covered it all. The problem should not exist. You may have hit on one other thing | as solderability of end termination area though non wetting will be clearly evident. One important detail is missing, what type of reflow oven you are working with? If it is a Convection type, then Mike suggestions should be enough but if it is an IR type, then try to turn the board direction by 90 or 180deg. Michael

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Earl Moon

#16456

Re: Film Capacitors - Tombstoning or Drawbridging Problems | 30 March, 1998

| | | | | We are having some problems with "drawbridging" on 0805 film capacitors. | | | | We have already reduced the pad width from .050" to .040" based on input | | | | from vendor. Defects appear to be random as far as location on the PWB and direction | | | | of placement. We are considering going to a pad width of .035" or less. Is anyone running | | | | this type of part without any problems? Is pad size the real key? Is there a recommended pad | | | | size? | | | From my experience I have seen four possible scenario that can cause this | | | 1) Component solderability (Find out what the plating is on the cap) | | | 2) Uneven heating (one end becoming liquidous before the other sometimes caused by heavy traces or a poor reflow profile) | | | 3) Component placement (to far to one end) | | | 4) Pad layout(try reducing the pad dimension beyond the cap termination, reducing the end pad dimension will reduce the amount of surface tension) | | | Lots of luck | | | Mike | | | | Mike covered it all. The problem should not exist. You may have hit on one other thing | | as solderability of end termination area though non wetting will be clearly evident. | One important detail is missing, what type of reflow oven you are working with? If it is a Convection type, then Mike suggestions should be enough but if it is an IR type, then try to turn the board direction by 90 or 180deg. | Michael I really like to zero in on prevention at the design and component selection level. Your one point concerning end termination solderability really hits home as too many component engineers are forced to by price without considering solderability. There is so much to say about this issue that cannot be said here without benifit of time or space. Earl Moon

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D.Lange

#16452

Re: Film Capacitors - Tombstoning or Drawbridging Problems | 17 April, 1998

| We are having some problems with "drawbridging" on 0805 film capacitors. | We have already reduced the pad width from .050" to .040" based on input | from vendor. Defects appear to be random as far as location on the PWB and direction | of placement. We are considering going to a pad width of .035" or less. Is anyone running | this type of part without any problems? Is pad size the real key? Is there a recommended pad | size? Hey David, Endcap not contact of paste on both ends (registration), insufficient "z" pressure on placement, and or excess time between placement and reflow (paste dry). That'll fix stonehenging! Doubt seriously you have to deal with respin.

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