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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


TH Crystals

#34150

TH Crystals | 9 May, 2005

Hello, I am hoping that someone can shed some light on my somewhat strange question. The group that I recently started with have had a process in place where they do not run crystals through their wave solder process. From my previous work experience, there was never a case where we would not wave solder something, especially crystals. The customer this process was created for requested that crystals be hand soldered as opposed to waved, so this has carried over to all new customers as a general process.

Is there any reason why crystals would not be run through the wave solder process?

All of my experience is with SMT equipment, and I have never touched a wave machine, and even my guys here are not sure why they don't wave crystals, they never investigated. Any information would be greatly appreciated!

Thanks in advanced!

-Todd Forbes

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#34163

TH Crystals | 10 May, 2005

We wave [primary side] and reflow crystals for oscillators without fear. We hand solder liquid crystal displays.

Consider checking with the crystal fabricator and using their guidelines.

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RDR

#34164

TH Crystals | 10 May, 2005

Are you running a water soluble process? There may have been an instance where a certain Xtal could not be washed. We have always waved Xtals like Dave without fear.

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tforbes

#34165

TH Crystals | 10 May, 2005

We are using a water soluable process, and we have no fear of washing the boards after the crystals have been placed. Any type of SMT crystal I have reflowed with no fear, thats why this practice troubles me, and I want to remove it altogether. I will see what I can get from the vendors, and perhapse I will run a profiler through the wave to see just what our pre-heat temperatures are.

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RDR

#34166

TH Crystals | 10 May, 2005

Maybe there is confusion between batterys and Xtals

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HOSS

#34167

TH Crystals | 10 May, 2005

One failure mode we have seen with TH XTALs is shorting from one of the leads to the metal can that houses the part. Typically, the opening around the lead at the base of the part can be small and if you combine this with a larger than needed annular ring, you have topside shorting.

Another problem can be vias under the part that can cause shorting. In either case a wafer insulator between the part and the PCB does the trick.

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#34168

TH Crystals | 10 May, 2005

We had an outside vendor that built a particular board for us. When there were problems with the new board 9 times out of 10 the case of the oscillator was shorted to the lead as mentioned in the post above. The fix would be to draw some of the solder out of the joint with copper tape which would pull the solder down off of the case.

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Rob

#34186

TH Crystals | 11 May, 2005

The above suggestions look to be the most likely, however on the off chance:

Going back a decade we saw damage to crystals & resonators due to induced harmonics from ultrasonics (usually in the wash).

Some fluxer systems use ultrasonics (I think Optiflux & Sonoflux do), and I do remember reading a paper about the use of ultrasonics in reducing the surface tension in a wave (I didn't need help sleeping that night) so I suppose it could be a pre-cautionary measure.

I also remember a range of KHz frequency products I used to look after when I was in manufacturers land that were "not suitable for use with ultrasonic production equipment".

Hope that helps,

Rob.

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tforbes

#34190

TH Crystals | 11 May, 2005

Thanks everyone! You gave me a lot of things to look at and investigate further.

Cheers!

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Lead Free Wave Solder - 1 Click SMT