identify a surface mount IC ???

SgtWookie

Joined Jul 17, 2007
22,210
I'm thinking it's a resistor divider IC.

You'll probably have to pull it off the board to test the individual circuits.
 

R!f@@

Joined Apr 2, 2009
9,682
Resistor arrays !!

Never seen that bugger before..

U have scratched IC...am thinking that board is from china or something..
 

SgtWookie

Joined Jul 17, 2007
22,210
The scratches could be laser trim cuts. They look fairly precise and repeated.
I do believe that you are correct. I didn't pay enough attention to that the first time around; I simply dismissed it as a covering for material underneath and didn't notice the cuts.

I'm somewhat surprised that it's not covered; that's sort of unusual. After laser trimming, it's customary for a lid to be attached in some manner so that the contents are protected.
 
It looks like the base of a switch pad, judging by the scratches. Or, if those are carbon film resistors, the missing media (scratches) are how they "trim" them in as stated above
 
There's an extra leg between each resistor, what could those be for? They're connected up so they must be for something...

Might be helpful to know what the board came out of too.
 

jimkeith

Joined Oct 26, 2011
540
There's an extra leg between each resistor, what could those be for? They're connected up so they must be for something...

There are likely resistors on the back side as well.

This looks exactly like hybrid circuits that I have worked with--the thick film resistor element is screened on to an alumina substrate and overcoated with a glass frit that is then fired to seal it--then it is laser trimmed to get exact resistance--the laser is so hot that it seals the edges of the cut
 

thatoneguy

Joined Feb 19, 2009
6,359
Is the device malfunctioning? The only way to fully identify and test it would be out of circuit/removing it, which can be a pain for a sensitive part in a working system.
 

ErnieM

Joined Apr 24, 2011
8,007
Definitely a resistor network. We use similar techniques here to make hybrid modules.

There are 3 resistors visible: 1,2<->15,16, 4,5<->12,13, 7,8<->9,10. You can even see their PCB lands have them common; they may be higher current resistors.

Now pins 3, 6, 11 and 14 also have active PCB lands and traces so they are not there for mechanical reasons, perhaps (probably) additional lower current resistors on the back.

The black material you can see is resistive paste; it is typically applied with a silk screen and fired in. Before that happens a metal layer would be applied, and each pair of pins would have a tab underneath the ends of the restive material so the resistor contacts metal and down to the pins.

The cut marks are due to a laser trim: the first pass makes the longer cut. This brings the resistor value up to but somewhat below the desired value. The seccond cut will have much less effect then the first cut as it is in what is called a "current shadow" area, and it acts as a fine adjustment. This is opposed to continue the first cut as at that point any additional cutting has a relatively large change in resistance.

Another way to make a fine adjustment is to make a right angle turn at the end of the first cut. Again, once you make the turn you are cutting into the shadow.

The resistance is determined by the ink used and it's surface resistivity, which is measured in ohms per square. Square what? Square nothing, if a square is 1 mil on a side or 1 mile on a side it has the same resistance. So by cutting the resistors as the picture shows you can guesstimate how many more squares the current path is. This given pattern may be used for a wide range of values.
 

Thread Starter

MattStrike

Joined Jun 12, 2010
14
I suspected it was a resistor, but hadn't seen a "z" following an "r" like that before. It is not malfunctioning, rather connected to a series of IC's that control 3 motors rotation from a fixed posistion. I am trying to isolate one of these motors and rebuild the circuit to be a standalone unit. Pins 6 & 14 are directly shorted according to my DMM. I will work on desoldering with hot air to get a shot at the back side. I assume the white base does not conduct so only have to measure the pins that are connected with the paste?
 
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