In a message dated 10/25/01 10:55:24 AM US Eastern Standard Time, [log in to unmask] writes:
What is "laser trimming of resistors"? According to the small research I
did, it's related to thick films. Is that true? What should I read on this,
starting with some on-line resources?
Keeping in mind that we are assemblers, not board manufacturers, how is this
trimming related to SMT assembly, what equipment would do it (at what cost),
implementation issues, etc.
All discrete surface mount resistors are trimmed to value by lasers. It is just that you can't see the cuts because the trimmed surface is overcoated with some passivation protection. Thick film hybrid circuits are trimmed "in the open" and you can see the trim to value. Interestingly, there is a move to embed resistors in circuit boards - in the middle of a multilayer. There is a proposal to laser trim these, too if high accuracy is required. Electro Scientific Industries (ESI) showed a concept machine for this at IPC Expo last April in Anaheim.
Both ESI and Lumonics make laser trim machines for the discrete component industry. With discretes, it is assumed the resistor is trimmed to the correct value before passivation coating (and sale) - do you have a need to change resistor values once the board is assembled? Can that be done by a variable resistor component?
Dennis Fritz
MacDermid