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Analysis of eight typical problems caused by optical modules’ assembly process

Date: 2019-10-16 18:43 From: C-LIGHT Onclick:
The prevalence of cloud computing and Internet of Things has created a higher demand for network speed, which has driven the prosperity of the optical module market. Optical modules, high-speed cables and active optical cables have been developed at a high speed. According to statistics, driven by the demand of mainstream 10G, 25G, 40G and 100G optical modules, the global optical module market is expected to reach $9.9 billion by 2020, and it is predicted that the port sales of 25G and 100G will be larger, the upcoming 200G and 400G optical module is also expected to maintain a certain market share. As the demand continues to increase, the optical module assembly process often encounters some different problems. C- light takes you to solve these problems. The followings are eight common types.
1.  Phenomenon description : the RX-ADC is 0 at the module’s receiver side
Reason analysis: RX-ADC is 0 which is mainly caused by no photo-generated current.
Maintenance methods:( 1) Check whether the ROSA and RSSI pins are Virtual welded or short circuited
(2)Check whether ROSA and VCC pins are broken.
(3)Check whether the RX high speed signal is short circuited
(4)Whether the foot of the Rssi and the anchor are short circuited
2.Phenomenon description: during the test IBiasADC is 0, TXLOP-ADC and RX-ADC failed.
Reason analysis: because of the PCBA design problem, filter capacitor of L1 and reference power on the power circuit to RX could be crashed or crushed .
Maintenance methods: replace PCBA board
3. Phenomenon description: short circuit of the module PCB board
Cause analysis: badly assembled snap fasteners or material problems
Maintenance method:
a. Check if the EMI tape on the top cover of the module is poked, causing a short circuit with the TOSA case.
b. Whether the ROSA foot is short cricuit to the body during the test
c. Test the TOSA body whether is short circuit
4. Phenomenon description: TX-LOP ADC Fail
Cause Analysis:
a, the PD pad on the soft board fail soldering (as shown)
b, TOSA's PD pin fail soldering (as shown)
Maintenance method: re-welding the position of the insufficient solder 
5. Phenomenon description: program writing failed?
Cause analysis: the program cannot be written in A0, and it is mainly related to EEPROM chip and MCU.WP: write control pin, low level effective.
Except WP, all other pin voltage of the measurement chip is normal. At the same time, WP is directly pulled to GND (PCBA itself WP pin is connected to MCU) and manually written into EEPROM information.It indicates that EEPROM chip has no exception.When WP is welded, EEPROM can be written normally.The final judgment is: PCBA problem.
Maintenance methods:
A. weld the WP again
B. Replace the PCBA and return the damaged PCBA to the supplier for replacement.
6. Description: the loop fiber test has a high working current, even above 1A (the module should be taken off the test board immediately if the current is found to be high)
Cause analysis: short circuit between Vcc and GND, which may be caused by internal connection welding of thermal pressure welding or soldered soft plate end of device pin.Low level effectiveness
Causes Analysis:
A.check Rosa directly with a multimeter.Are Vcc and GND short-circuited?LD+ and LD- short circuit to ground.
B. If the short circuit requires removal of Rosa or Tosa, is it due to poor thermal pressure welding or short circuit at the solder end of the device??
Maintenance method: poor hot pressure welding : redo the whole process;replacements of faulty parts?
7.Description of the phenomenon: all data of loop fiber testing software are 514 or 261, and the power current is normal or small?
Cause analysis: PCBA single - chip computer did not burn procedures, poor incoming materials?
Checking method: use Debug software to see that DMI is all 0 or inf
Maintenance method: a. replace the PCBA and return the defective products
8. Phenomenon description: In the loopback fiber test software, TXLOP-ADC and RX-ADC not passed.
Reason analysis: Tosa welding is poor; Tosa itself does not have light, poor performance; Tosa soft board broken; Tosa end face unclean
Inspection Method:
a. Check if Tosa has a virtual weld.
B. optical power meter check Tosa? Whether it shines
c. the multimeter checks whether the soft board is broken
Maintenance method:
a. the virtual welding removes the device to reheat the welding;
b. poor performance of the device, no light and soft board break replacement device.
optical modules
C-light’s provides professional, high-quality and cost-effective optical fiber module products, which are compatible with huawei, zte, Cisco, H3C,Brocade, alcatel, Finisar, Avago Avago, HP , INTEL, etc. The optical module speed covers 155M,622M, 1.25g, 2.5g, 6G, 8G, 10G, 40G and 100G. Support for SFP,XFP,CFP,QSFP and other packing. They could widely used in various fiber switches, fiber network CARDS, SDH, servers and other communication brand equipment.

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