Factors to consider when choosing an alignment system

A lthough an economic analysis will usually show that process-yield improvements and cycletime considerations have a far larger effect on the total cost of ownership, price is usually seen as the most important consideration when choosing an alignment system. Yet price should not be the single determining factor. True, system improvements to increase coupling yield are limited by prices that the market will bear, which creates an inevitable tradeoff of cost versus performance. An alignment system manufacturer could make the translation stages out of very-low-thermalcoefficient-of-expansion materials like Invar and the thermal effects would be drastically improved, but the system would cost too much. On the other hand, inexpensive stepper motors could be used, but the poor inherent repeatability and high thermal outputs would have a negative effect on coupling yield. Thus, the most economical system would have high coupling yield without becoming prohibitively expensive. Since most alignment algorithms must pass through the “peak” point during the alignment process to determine that component positioning is indeed at optimum, the coupling yield depends on the ability of the alignment system to repeatedly return to that point (a function of the motion system) and the ability to maintain thermal and mechanical stability during and after the alignment process (a function of the thermal loads and mechanical design of the system).