lightable production status id week october 2014 tony weidberg1

Tony Weidberg 1

LightABLE Production Status

ID Week October 2014


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LTx Project

• Aim: use commercial package for VCSEL array to improve reliability.

• LTx installed in crate 3 – BER from long physics

mode run ok– Problems with calibration

runs, required manual tweaking of MSR (slow!)


LightABLE OSA (Reflex Photonics)

Production Status

• 500 LightABLEs delivered. • Assembly completed at Oxford.• Yields much lower than anticipated from

preproduction batch of 20– Mistakes in assembly procedure– Open circuits inside BGA after reflow process

• Hypothesis: due to delay between dryout and storage in dry N2.

– Total optical power high but OMA below threshold.

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Numbers• Available:

• 20 LTx which failed xBPM test being recovered by Mark.• Ordered 50 more LTx.

– Will be much more careful with all production steps expect higher yield.• Have ordered 50 LightABLE (8-12 week delivery)

– Z board and LightABLE PCBs assembled with all the other components.


Cambridge QA yield 0.83installed crate 3 44at CERN 26cat A&B @ Cambridge 156 5at Oxford 146 121Rick recovered 3Total 355Required 354

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Backup


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Changes Since Design Review

• Essential: – Make it easier for Infineon SMC connector to

connect to LTx in USA15– Improve thermal management

• Highly desirable: Allow option of decreasing optical power from LTx in case of saturation for DORIC4A.

• Mechanical reliability, consider use of under-fill for LightABLE BGA.


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Mechanical Changes• Make mate/demate with Infineon

SMC easier.– Shortened length of MT guide

pins.– Added groove near end that was

cut to help with gluing. End sticking out is the uncut end.

– Use long guide pins in jig during reflow. Ensures that guide pins will be in the correct location and pointing the correct way.


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Underfill

• Decided against use of underfill for BGA– Mismatch in CTE.– Very little insertion force required.– 100 mate/demate cycles with monitoring of power every

10 cycles no changes– Thermal cycling: no change in power.


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Cooling• Thermal path from LightABLE to front panel

via Thermal Gap Filler (3 Wm/K)• OSA analysis DT from junction to ambient

=20°C ( next slide).


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OSA Analysis

• Measure Peak wavelength lp• Scan Mark: Space Ratio (MSR)

and measure lp• Plot lp versus MSR• Fit slope and extrapolate to

50%.• Use calibration dlp/dT DT• Fit Results variable in quality

but reasonable consistency


Tony Weidberg

AtLinks LightABLE- uProc

We can use a microprocessor to drive the LightABLE Engine’s I2C inputs, and the SPI lines currently used for the MDACs can be used to drive the µProc

But the MDACS we must still give the right output current for the interface circuit• This could be done using the µProc’s SPI lines• It could be carried out when the µProc is initialised• The MDAC_CLR command (one of the BOC_SPI signals) could be

used to force a uProc initialisation

This is what it would look like:

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Maurice Goodrick

Tony Weidberg

AtLinks LightABLE- uProc Connections

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Z PCB

Maurice Goodrick

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QA: Optical Power


1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 More0

5

10

15

20

25

30

35

40

45

LTx

Power (mW)

Freq

uenc

y

-2.4 -2 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2 2.40

5

10

15

20

25

30

35

40

LTx

After - Before Burn-in (dB)

Freq

uenc

y

<Optical Power> @ 50% duty cycle,after burn-in

Change with burn-in (72 hours @70C)

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LTx in SR1

• LTx optical power.• No T correction• Initial decrease

~1%.– No burn-in

preformed for this array probably ok but should run longer

Steve McMahon

Opti

cal P

ower

(mV)

Time (days)ID Week October 2014

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Steve McMahonO

ptica

l Pow

er (m

V)

Time (days)ID Week October 2014

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Summary

• Improvements following design review have been implemented.

• Production well underway.• Populate one crate in USA-15 in May• Need to continue long-term optical power

monitoring in SR1 and USA-15.


Backup Slides

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OSA Thermal Studies• New metalwork for front panel of BOC

– Takes heat through thermal pad metalwork outside crate• OSA measured for 12 channels from first LTx with micro on board.• OSA spectra taken at MSR settings of 0, 10, 20 and 24 (maximum

value which gave clean waveform).• Very crude peak finding

– Found lmax corresponding to maximum power

– Found l1 and l2 corresponding to peak power -3dB

– Best estimate lpeak= (l1 + l2)/2

– Used difference between lpeak and lmax as estimate of error.– Error on MSR set to 1% (guess)– Fit lpeak vs MSR next slides


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Fit Results variable in quality but reasonable consistency


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Check this point (see next slide)


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Check Channel 8 MSR=20• Spectra looks ok• Programme found reasonable results• 3 sigma effect doesn’t change conclusions

855 855.05 855.1 855.15 855.2 855.25 855.3 855.35 855.40.00E+00

5.00E-03

1.00E-02

1.50E-02

2.00E-02

2.50E-02

3.00E-02

3.50E-02

ch 8 MSR=20

ch 8 MSR=20

From programme:Max power @ 833.330 nmPeak @ 833.327 nmLooks ok?


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Summary

• Fits to each channel for slope• Use Carlos’s analysis for temperature

sensitivity– dl/dT=0.0673 nm/K

• Extrapolate to 50% duty cycle• DT = 20 ± 4 C• Improved thermal performance compared

to previous study DT = 29 to 43 C. – Improved metalwork takes heat through

thermal pad to outside of crate.

channel slope

0 0.0273

1 0.0235

2 0.0242

3 0.0296

4 0.0241

5 0.0251

6 0.0260

7 0.0251

8 0.0445

9 0.0271

10 0.0280

11 0.0259


lightable production status id week october 2014 tony weidberg1

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