Golden ppms of December

This week we can look inside of the resistor network from Vishay Precision Group, Model 1442 also known by marketing name PRND. It is build using BMF elements, more commonly known by their famous VHP resistors. But unlike VHP resistors these networks are made to order only, with customer specified values and specification requirements.

PRND and high temperature variant PRND HT are available in different hermetical packages, such as CERDIP8, CERDIP14 and CERDIP16, Gullwing CERDIP8/14/16, 16-pad ceramic LCC and 14-lead Flatpack. All of these have ceramic package with soldered metal lids. There are many more package variants also available from VPG for custom designs.

Two square LCC chips are not rumored ADR1001 but bit more special Analog Devices 77052012X. This is low leakage 8-channel ADG508A analog multiplexer in mil variant. These switches rated for supply voltage up to ±22V, continuous current up to 20mA and have RON resistance around 200 Ω with ±15 V supply. Other than hi-rel package and tighter quality control they are same as commercial part.

Teardown of hermetic package like CERDIP is very easy. No need for dangerous acids or precision machining, just use sharp side cutters to crack top lid off the soldered ceramic carrier and we are in. Package is 94% alumina (Al2O3) with gold plated kovar lid and Alloy 42 (Iron Nickel) terminals. Terminals are gold plated with 100 µinch layer.
Because these resistors acquired from secondary market, it is unclear if this particular network regular type PRND or PRND HT.

318828 using four V15×5 resistor chips. Each chip is bonded to terminal contact pad by thin gold wires.

There are few markings on each chip. All four have mark VIL 9B, perhaps internal part number for particular design. There is also coded number 2513 which suggests 25.1 kΩ element on outer chips, and 494 which suggests 4.9 kΩ center element if these codes resemble typical SMD marks. It is visible that center element has more coarse pitch of resistive metal layer artwork, hinting at lower resistance.

We can study datasheet for these resistive chip elements for more details. These chips are essentially network of foil resistors with possibility to short sections to obtain necessary ohmic value between two gold plated pad terminations. Trims are cut mechanically or with laser, increasing resistance of the chip. By having large number of trim points resistance value of each chip can be set in “digital” manner during fabrication.

5×15 element has 20 trim points, some of which are visibly cut on our network chips. Vishay Precision Group actually sells these V5×15 and other size elements for customers per special requests as well, if somebody wants to integrate resistive elements in their chip/hybrid design.

Initial measurements of these custom networks with Keithley 2002 revealed final values shown below:

And if you thought that VHP100 resistors at $50 USD per piece were expensive, PRND networks are just next level, with starting price at US$160/pcs.

Author: Ilya Tsemenko
Created: Dec. 10, 2022, 1:41 a.m.
Modified: Aug. 12, 2023, 8:35 p.m.