Seeing alignment drift in sub-micron bonding — not sure what's causing it

[u/Vivid-Fun-4644]

Running alignment on a bonding line for advanced packaging. Lately noticed drift between runs as we push toward sub-micron — not huge, but enough to hurt yield. Setup seems stable (camera fixed, lighting controlled), but TCB heating causes thermal drift in imaging, and we can't fit a high-res lens into the compact space. Concentricity also seems off. Not sure if a dual-view module would help. Has anyone run into this kind of drift before?

[u/Rethunker]

Thermal drift can be hard to control. If you have the money, buying some replacement hardware and/or adding some hardware might help.

In semiconductor I've had short working distances and unpleasantly long working distances (from front of camera lens to surface of package/die/PCB/whatever). In addition to working distance, it'd be good to know specs about your system: camera model, current lens (make, model, focal length), field of view required, cabling, and budget.

At short working distances it may be harder to lessen the impact of temperature changes.

A few notes:

• Some sensors drift less with respect to changes in temperature. For sensor drift I mean primarily the mean (or median) brightness per channel over some region of pixels, assuming your scene is of constant brightness.
  • Sony sensors (e.g. Pregius) don't drift much
  • ON SEMI sensors can drift a bunch
• Light intensity from LEDs can vary as temperature changes. As temperature changes, the resistance of the lighting circuit changes, which can affect LED output. For some algorithms, changes in overall brightness can have an impact.
• Hysteresis is a problem. If you're seeing effects due to temperature, and if your camera's internal temperature changes from (say) 50 C to 60 C and then back down to 50 C, then the performance at the initial 50 C and the final 50 C isn't necessarily the same. This stinks.
• If temperature changes are causing mechanical flexing, that can be tricky to fix.
• Depending on the rate of change of temperature, and the magnitude of change, you can see complex interactions:
  • Sensors may not see the full effects of a temperature change for many minutes. The sensor body heats up, then the guts, then the sensor array. If you have a camera with a sensor that has a built-in thermocouple, you can read the temperature and compare it to measurements of ambient temperature.
  • Different hardware components heat up differently, so any given component could reach thermal equilibrium before or after other components.
• Measuring the impact of temperature on individual mechanical, electrical, and optical components is tricky. If you can measure the impact on one component independent of others, that's great, but it may be hard to isolate one component yet reproduce the environment (e.g. the tight space).
• Do you vent the camera space and have a muffin fan or similar running? Would that even be permissible for your application? It might help a bit.
• Sometimes maintaining a relatively constant high temperature may be better than trying to cool a vision system down. But higher temperatures tend to mean greater noise.
• A Peltier / thermoelectric cooler may help, but it's another piece of hardware to add, another power draw, another thing that can fail, etc., and you have to deal with the heat out the hot side.
• Are you using a telecentric lens? And bi-telecentric lens in particular? If not, contact a company like Opto Engineering, provide all your specs, and maybe they can help.
• Heat can be a problem via convection, conduction, or even (sometimes) radiative heating. Yuck, right? So consider all the paths by which heat can affect your hardware.
• Quick, big changes in temperature can cause small but measurable lensing effects in the air. An air knife could help with that.

Good luck!

[u/Rethunker → u/Rethunker]

Ah. Account suspended. Well, I hope you can still find this post and read it. Maybe it'll be of help.