Notice for soldering and mounting

Technical Note of Crystal Units
- The points of designing PCB layout -

For PCB layout
When you design PCB layout, it is necessary "1) to prevent decreasing negative resistance" and "2) to prevent EMI problem".

Pattern length of oscillation circuit
The length of signal patterns in oscillation circuit should be as short as possible to minimize stray capacitance/inductance Through-holes should not be applied to oscillation circuit because it causes large EMI.

Influence by pattern around oscillation circuit
Ground or signal path should not be located in the middle layer of multi-layer circuit board to overlap the oscillation circuit as the stray capacitance between ground and oscillation circuit becomes large.
Large stray capacitance may cause oscillation stop due to insufficient oscillation margin. The signal path located close to the input of C-MOS inverter may generate EMI as a noise in waveform is amplified.

Electrical shield by ground pattern
If you place a ground area for electrical shield, place it on the opposite surface of circuit board to the oscillation circuit. A ground pattern in the middle layer may cause oscillation margin as discussed above. The ground pattern around oscillation circuit shall not be too close to the oscillation circuit to prevent large stray capacitance.

Ex) Oscillation circuit, Ex) Parts placement

Ex) Signal line is close to circuit, Ex) GND area is in next layer

Ex) Pattern length is long, Ex) Through-hole is used in pattern


- The points of mounting crystal unit -


Mechanical stress

For crystal unit mounting, it is recommended to employ machines with optical positioning capability to prevent applying excessive mechanical stress.
Make sure that you have evaluated by using placement machines before going into mass production. Do not use machines with mechanical positioning.

Soldering

Solder the crystal unit by re-flow soldering.
Refer below table for our recommendable flux, solder and soldering profile.

Recommendable Flux and Solder
Flux Please use rosin based flux, but do not use water soluble flux.
Solder Please use solder (Sn-3.0Ag-0.5Cu) under the following condition.
Standard thickness of soldering paste: 0.10 to 0.15mm

Recommendable Flux and Solder

  Standard soldering profile
Pre-heating 150 to 180℃
60 to 120s
Heating 220℃ min.
30s to 60s
Peak temperature 245℃ min. 260℃ max.
5s max.
Component shall measured on the surface.

Washing / Corting
Conformal coating or washing cannot be applied to the crystal unit as it is not hermetically sealed.