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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Solder Balls

Neil Stoddart

#4523

Solder Balls | 4 April, 2000

Help.

We are moving to a no clean solder paste and have the following concerns regarding solder balls.

What standards are currently being followed concerning solder balls on SMT assemblies? Are these standards realistic and can they be easily achieved? What is the maximum permissible size for a solder ball and how do we inspect them.

Our current production facility does not have the ability to X-ray and only has limited vision equipment

Any information will be gladly appreciated.

Regards

Neil.

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Donnie

#4524

Re: Solder Balls | 4 April, 2000

Neil, We currently use only visual inspection with a magnified lamp and actually brush the board after the wave process to help knock off any solder balls. You wanna use an ESD sensitive brush material. Camel hair is what we use. It works real well. As for what size is acceptable, I really can't tell you much there. I would say that there should be zero since they can break free and get in between solder joints and leads. Hope this helps some.

Donnie

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RDR

#4525

Re: Solder Balls | 4 April, 2000

Neil, IPC 610 has the criteria for solder balls re. quantity and size per sq./in. These are acheivable requirements but no-clean is not necessarily a drop in process. You need to review stencil /pad /component design to ensure that "midship" solder balls do not occur during the reflow process. Wave soldering is a different story and I agree with Donnie that you will probably need to brush the assemblies after wave. Proper flux selection and soldermask material along with solid profile development are key to minimizing these balls.

Good Luck

Russ

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Matthew Amidon

#4526

Re: Solder Balls | 8 April, 2000

Make sure your screen aperture size is about 80%, and you should not have a problem.

Some pastes require a hump profile, to get rid of balls.

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