Array Resistors

resistor array displays in SIP package

image source is from: www.reliablelectronics.com/images/SIP_Iso_Res...

Array Resistors - Array resistors are specifically just a combination of resistors made and compacted into one package for the purpose of containing a single composition of series of resistors but of multiple uses and functions to add functionality to the circuit boards where you can use it on many purposes as intended. Sometimes the array resistors are called as array chips and sometimes chip resistors or its combination, the chip array resistors. Some manufacturers and suppliers have it labeled as the (BGA) or ball grid array. Common sources and manufacturers come from either China, Taiwan or India because of the low labor costs and cheap raw materials to use and adapt for the array resistor manufacturing. These array resistors also come in two different packages such as the SIP and DIP package. Each of this array resistor package serves its purpose and use depending upon the need of the circuit board design and component placement.

resistor array display in DIP package

image source is from: www.reliablelectronics.com/images/Hm_Pg_Dip_A...

An article from wikipedia about the relevance of BGA's is discussed here - http://en.wikipedia.org/wiki/Ball_grid_array

Advantages

High density

The BGA is a solution to the problem of producing a miniature package for an integrated circuit with many hundreds of pins. Pin grid arrays and dual-in-line surface mount (SOIC) packages were being produced with more and more pins, and with decreasing spacing between the pins, but this was causing difficulties for the soldering process. As package pins got closer together, the danger of accidentally bridging adjacent pins with solder grew. BGAs do not have this problem, because the solder is factory-applied to the package in exactly the right amount.

Heat Conduction

A further advantage of BGA packages over packages with discrete leads (i.e. packages with legs) is the lower thermal resistance between the package and the PCB. This allows heat generated by the integrated circuit inside the package to flow more easily to the PCB, preventing the chip from overheating.

Low Inductance leads

The shorter an electrical conductor, the lower its inductance, a property which causes unwanted distortion of signals in high-speed electronic circuits. BGAs, with their very short distance between the package and the PCB, have low inductances and therefore have far superior electrical performance to leaded devices.

BGAs find some use in security-sensitive applications, especially where it is impossible to prevent physical access to the chip. For instance, a ROM chip with a BGA configuration is considerably more difficult to access than one in a DIP or TSOP layout. Tracing circuit paths to the BGA chip is limited by the contact points being obscured by the chip itself.

Disadvantages

X-ray of BGA.

Non compliant leads

A disadvantage of BGAs, however, is that the solder balls cannot flex (non-compliant) in the way that longer leads can. Bending, due to a difference in Coefficient of thermal expansion between PCB substrate & BGA (thermal stress), or flexing & vibration (mechanical stress) can cause the solder joints to fracture. BGAs are therefore unpopular in certain fields, such as aerospace and military electronics. This problem can be overcome, at a cost, by matching the mechanical and thermal characteristics of the PCB to those of the BGA.

Expensive inspection

Another disadvantage of BGAs is that, once the package is soldered down, it is very difficult to look for soldering faults. X-ray machines and special microscopes have been developed to overcome this problem, but are expensive. If a BGA is found to be badly soldered, it can be removed in a rework station, which is a jig fitted with infrared lamp (or hot air), a thermocouple and a vacuum device for lifting the package. The BGA can be replaced with a new one, or can be refurbished or reballed. Packets of tiny ready-made solder balls are sold for this purpose.