Looking for Hall effect sensor with sense element on IC bottom

[halexa]

Hi,

I'm looking for a solution were we want to detect a steel rod end position under a PCB. Todays solution is a hall sensor mounted on the bottom if the PCB as shown in picture 1.
I want to cut production cost and mount all components on the top side of the PCB so I'm looking for a solution to mount the sensor on the top side. Shown in picture 2.
Do someone out there know if there are hall effect sensors with the sensing element on the bottom of the IC.

To bend a TO92 or mount SOT23 upside down is not an option.

Today we use VF360ST from Honeywell.

[tatus1969]

as magnetic flux passes through the entire sensor anyway, I would expect that you easily can use a regular one like yours in SOT23 without any degradation in sensitivity. Just make sure to use the other magnet pole when not using a bidirectional one.

[AndyC_772]

Right. Mounting it on the top of the board just means it's a bit further away from the rod, that's all. Provided it's sensitive enough that it'll work reliably over the greater distance, swapping sides is a non-issue.

[halexa]

Thx for the  feedback.

I will do a bench test with a SOT23 with oposite magnetic polarity mounted on the top side. And see if i can get a good signal.

[MosherIV]

What about a small cut out in the board so the sensor can be soldered to the top side but be pointed through the hole in the board?

Just throwing the idea out there.

[AndyC_772]

It's sensing magnetic fields. Why would a fibreglass PCB need a hole in it?

[Ian.M]

It's sensing magnetic fields. Why would a fibreglass PCB need a hole in it?

To reduce the range by the height of the Hall sensor package above its leadframe.
Probably wont make the slightest difference unless one is sensing very small objects.

[halexa]

What about a small cut out in the board so the sensor can be soldered to the top side but be pointed through the hole in the board?

Just throwing the idea out there.

Not an option since then the IC then has to be mounted opside down and I don't think that will be an easy task for the pick and place machine.

[tatus1969]

how is that setup meant to work anyway? You can't measure presence of a steel rod with a Hall sensor, unless that steel is magnetized. That would need to be accomplished with an inductive proximity detector. I happen to work on one (price point < 5USD) and could share the circuit.

[Edsoncan]

Is  it not possible to use a LVDT sensor?
http://www.te.com/usa-en/industries/sensor-solutions/insights/lvdt-tutorial.html