Varistor-Lead count and spacing-Specifications-PCB

- Feb 17, 2017-

Varistor-Lead count and spacing-

Specifications-PCB

Quad in-line

A Rockwell 6502-based microcontroller in a QIP package

Rockwell used a quad in-line package with 42 leads formed into staggered rows for their PPS-4 microprocessor family introduced in 1973, and other microprocessors and microcontrollers, some with higher lead counts, through the early 1990s.

The QIP, sometimes called a QIL package, has the same dimensions as a DIL package, but the leads on each side are bent into an alternating zigzag configuration so as to fit four lines of solder pads (instead of two with a DIL). The QIL design increased the spacing between solder pads without increasing package size, for two reasons:

  1. First it allowed more reliable soldering. This may seem odd today, given the far closer solder pad spacing in use now, but in the 1970s, the heyday of the QIL, bridging of neighbouring solder pads on DIL chips was an issue at times,

  2. QIL also increased the possibility of running a copper track between 2 solder pads. This was very handy on the then standard single sided single layer PCBs.

Some QIL packaged ICs had added heatsinking tabs, such as the HA1306.

Intel and 3M developed the ceramic leadless quad in-line package (QUIP), introduced in 1979, to boost microprocessor density and economy. The ceramic leadless QUIP is not designed for surface-mount use, and requires a socket. It was used by Intel for the iAPX 432 microprocessor chip set, and by Zilog for the Z8-02 external-ROM prototyping version of the Z8 microcontroller.

Lead count and spacing

Commonly found DIP packages that conform to JEDEC standards use an inter-lead spacing (lead pitch) of 0.1 inch (2.54 mm). Row spacing varies depending on lead counts, with 0.3 in. (7.62 mm)(JEDEC MS-001) or 0.6 inch (15.24 mm)(JEDEC MS-011) the most common. Less common standardized row spacings include 0.4 inch (10.16 mm)(JEDEC MS-010) and 0.9 inch (22.86 mm), as well as a row spacing of 0.3 inch, 0.6 inch or 0.75 inch with a 0.07 inch (1.778 mm) lead pitch.

The former Soviet Union and Eastern bloc countries used similar packages, but with a metric inter-lead spacing of 2.5 mm rather than 2.54 mm (0.1 inch).

The number of leads is always even. For 0.3 inch spacing, typical lead counts are 8, 14, 16, 18, and 28; less common are 4, 6, 20, and 24 lead counts. For 0.6 inch spacing, typical lead counts are 24, 28, 32, and 40; less common are 36, 48, 52, and 64 lead counts. Some microprocessors, such as the Motorola 68000 and Zilog Z180, used lead counts as high as 64; this is typically the maximum number of leads for a DIP package.


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