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How long can solder sit on panel

Views: 2273

#78639

How long can solder sit on panel | 9 August, 2017

I have a question for the experts. After a panel is printed, how long is too long for the panel to sit prior to reflow? I understand each paste will be different, wondering if there is a general rule of thumb?

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dwl

#78640

How long can solder sit on panel | 9 August, 2017

As you already know, it depends on the paste. There isn't really a rule of thumb, but less time exposed it better.

The issue is the flux exposure to the air and ambient conditions. The flux can evaporate or absorb moisture from the air. If the paste sits out too long, you'll start to have defects like solder balls, poor wetting, bridging of fine pitch parts, and increased voiding.

is there a specific reason for asking?

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#78641

How long can solder sit on panel | 9 August, 2017

It also varies with the types of deposits. Small deposits of paste (as seen on fine pitch parts or small chips) seem to be more affected by exposure. Jerry

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#78643

How long can solder sit on panel | 9 August, 2017

Trying to show documentation/expert opinion to an operator or 2 why it's important to not let a first piece, that they so diligently built for the next shift to let sit for an hour, why that's not a good idea...other than me telling them so. And telling them common sense dictates.

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dwl

#78658

How long can solder sit on panel | 10 August, 2017

You could always take a scrap board, paste it, and let it sit out over night. Reflow it and then you should have a nice visual aid, covered in solder balls and grainy, irregularly shaped solder mounds.

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#78695

How long can solder sit on panel | 14 August, 2017

In my experience, in a temperature/humidity controlled environment, 1 hour, no big deal. 4 hours still ok. Overnight your pushing the limits but will probably reflow without issues. Any longer, could be a problem.

Again, a lot depend on type of paste, aperture size and stencil thickness, etc.

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#78700

How long can solder sit on panel | 15 August, 2017

Most important factor - temperature. Back in the days I worked for a place without AC, and summer time this paste couldn't make it for more than an hour. In controlled environment you will be safe for hours or even a shift.

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