Q:

Reasons for 741 op-amp latching up?

what does 741 operational amplifier latch up mean? what are the reasons IN GENERAL for that? i need a general answer only

A:

The attached is a sketch of a dual well CMOS process cross-section contrived to show a parasitic structure known as a SCR.

The diodes shown are junctions that are present and the red line shows a current path that starts on (for example) Signal 2, contacts to P++ S/D implant, moves through NWell into the PWell and then finally into the N++ S/D implants into the contacts for signal 1.  That describes a PNPN structure which is also know as a A SCR (Silicon controlled rectifier).
This is a parasitic structure that exists in ALL modern processes and must be accounted for during design by following what is known as design rules for spacing.  You're not allowed to place different structures too close together for example.
An SCR, once triggered will "latch-up" and conduct current until the current path is broken.  In the case of a chip, this either when the power supply fails or the chip self-destructs.  The wells are very large structures and can handle large amounts of currents so once activated they win out over any deliberately designed structures.
I don't know the details of the process used to fabricate the '741 but I show the CMOS process example as a cautionary tale that a parasitic SCR does exist even in todays modern CMOS processes even after all these years -- it is inherent.
In general a device will latch up when the parasitic device is triggered by voltages being out of range.  In my sketch signal 1 would need to exceed Vdd and Signal 2 would need to be lower than ground and the SCR depends upon doping levels and electric fields and spacing.
Reading the 741 specification and observing its limits in normal operation is advised.  Although it would be educational to sacrifice a few of these devices in an experiment.
Regardless of what people think of the 741, it is a nice starting point to understanding simple op-amps and contains the key element of what is the core of an op-amp the "differential pair".

