Film-type resistor networks are often employed in electronic circuits and are usually laser trimmed to desired resistance values. Typically, a network of deposited film resistors is formed on a small ceramic substrate, and after formation the resistors are trimmed by selective volatilization of resistive material caused by laser trimming apparatus to thereby adjust their resistance. The trimmed resistor network is thereafter installed on the substrate of an associated circuit or header containing leads or contacts for connection to external circuitry. Electrical connections between the resistors of the network and corresponding connection points on the associated circuit or header are usually provided by wire bonding. The thus assembled circuit package is then encapsulated or otherwise enclosed for protection. The resistor network is sometimes mounted on a header or a support and thereafter trimmed. Tolerance variations in the overall support can cause variation in the height of the network sufficient to affect the performance of the trimming operation. The height of the network can vary by 0.005 inch or more, as a result of which the laser source will not be in precise focus or must be refocused for the particular network to be trimmed.
It is often disadvantageous that the resistor network must be trimmed prior to final assembly in an associated circuit or header, and cannot be trimmed after such final assembly. As a consequence, while a resistor network can be trimmed to a predetermined specification, the network in association with an overall circuit may not be within intended specification. Similarly, a trimmed network after incorporation into an associated headed may not be precisely within specification by reason of parameter variations caused by the assembly procedure. The use of wire bonding is also a disadvantage in conventional circuit packaging techniques. Manual or semiautomatic wire bonding requires a skilled operator and carefully controlled equipment. Automatic wire bonding requires the use of extremely expensive equipment which requires careful set-up to achieve intended performance. Moreover, the wire bonds are themselves very delicate, and great care must be exercised in enclosing a resulting wire bonded package to prevent breakage of the wires.