16Mhz and 32.768Khz Crystal Problem in Mass Production

Hi,

Crystals at our products stop running after mass production.
We didn't live same problems with prototype.
Did you live any experiency like this? and How can we solve this problem?

Thank you.

It can be that the load capacitor is of wrong value. to debug you can just change the capacitor in one of the board and test.
or another cause may be the wrong soldering technique.. may be you are using very high temp for soldering.. go through the data sheet .. you will surely find something.

khanna_gunjan said:

It can be that the load capacitor is of wrong value. to debug you can just change the capacitor in one of the board and test.
or another cause may be the wrong soldering technique.. may be you are using very high temp for soldering.. go through the data sheet .. you will surely find something.

Click to expand...

Manufacturer of the crystals told us that "you should use 180Cdeg temperature and 3 seconds to solder them." But we can't solder them at this temperature and period. We use 250C and 3.6sec at crucible when mass production. Does this cause the problem?

An other problem, how can We be sure that if load capacitors of the crystals are at wrong values? We used two 22pF for 16Mhz and 18pF, 22pF for 32.768Khz.

Thank you.

yes the soldering can be one of the prob. also try changing the load capacitor in one of the board and see if it works.. if possible put the same value caps as you have in your prototype board.

for soldering you can try soldering them manually after all other components are soldered.. i assume you are using automatic soldering process for the mass production

khanna_gunjan said:

yes the soldering can be one of the prob. also try changing the load capacitor in one of the board and see if it works.. if possible put the same value caps as you have in your prototype board.

for soldering you can try soldering them manually after all other components are soldered.. i assume you are using automatic soldering process for the mass production

Click to expand...

Do you know how I can measure the power of across the crystal pins?

Hi,

Sentivity to load caps greatly depends on the actual crystal that you are using. I found out that the crystal manufacturer engineers are often very helpful with this kind of situations. They can also tell you if the soldering process that you are using can be the source of the failure.

From my experience, the oscillator isn't that sensitive to the load capacitor value, but if you use a value that is already on the edge, it is still possible that the stray capacitance of the PCB makes the oscillator unstable.

Good luck,

cyberblak

we had this problem once when we populated a resistor in the circuit incorrectly - are you using any external resistors with the crystal?
Also we learned that it is important to route all signals on the same side of the PCB as the components (with no vias).

i had a similar problem
and we changed the capacitor's value to lower value of capacitance.
anyway you need to check in scope the Vpp on the Oscilator's pins
you will see the answer right away....