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Solder balls under LLP

Views: 1692

S vaughan

#36341

Solder balls under LLP | 26 August, 2005

Hello,

Can anyone comment on the implications of small sodler balls under a leadless device such as LLP with a centre thermal land. I believe that we did not make a good reduction and the paste squeezed out of the centre land and balled up under the part. Everything seems Ok- no shorts but X-ray does show the balls. Is this a defect or process indicator?

thanks

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#36351

Solder balls under LLP | 26 August, 2005

Hello there, Most probably, since the solder balls are entrapped, it is a process indicator, but refer to IPC 610-6.5.3.1 on Excess solder / solder balls / splashes - it really depends on what class you are manufacturing, and the minimum electrical clearance you must meet. It is only a defect if solder balls VMEC (violate minimum electrical clearance).

Regards, Sara Rice Foresite Inc. www.residues.com

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#36360

Solder balls under LLP | 28 August, 2005

Sara Rice: How did you determine the balls were entrapped?

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#36374

Solder balls under LLP | 29 August, 2005

davef: I am a colleague of Sara at Foresite and we came to the conclusion that the solder balls were entrapped based on the minimal amount of information from the original question and the fact that the x-ray showed the balls and it wasn't mentioned that they were visible on any other are of the assy. From my experience if there are solder balls under a leadless component they will be entrapped either due to size or flux residues holding them in place. In either case, once again depending on size, they are a process indicator as long as there is no VMEC.

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#36381

Solder balls under LLP | 29 August, 2005

Hi All,

In IPC-A-610 there is a definition for what constitutes "Entrapped/encapsulated/attached" on page 5-14 in the note. It says that it means that the ball will not be dislodged in the normal service environment of the product.

Jim Jenkins

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#36439

Solder balls under LLP | 31 August, 2005

I have been having the same problem with the LLP. I have three stencil I have done reduction on. The first I went by the manufacturing recommendations. The last two I have done more reducing for the thermal pad. The last one was at a 20% reduction and I still had solder balls. If you find a solution please let me know. Thanks

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RDR

#36454

Solder balls under LLP | 1 September, 2005

Thermal pads located underneath leadless devices require a 50% reduction in the stencil aperture.

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URL

#36462

Solder balls under LLP | 1 September, 2005

Unless it is peppered with via holes. Then it depends on the size of the pad and via holes.

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