How To Select A Test Probe Tip?

We wrote this essay for our test engineers to pick up the suitable and better Spring Probe head Tips.

In common cases, there are 3 main testing situation for ICT( in-circuit test)

Soldering Spot, Via Hole, Dip.

Of course, some OEM/ ODM manufacturers will have a testing on some connectors or metal pin plugs.

Ok, here we should have a rough impression about what we would test.

We could look at the illustration about a soldering spot. Different Manufacturers have different soldering process about PCB. But normally they look like those 3 situations. The pad is generated after the SMT process, and high temperature is going down, and FLUX is flowing out of the Tin spot, you know the liquid scaling powder or flux is covering the pad surface finally, and FLUX is not easy to puncture and it is not conductive.

------------------------------------------Soldering Pad- Test Probe Tip Selection------------------------------------------

Situation "a": Called Flate Pad. It comes easily to test because the flux covering the pad evenly spot.

Situation "b": Called Arc Pad. It is not hard to test when we use a right head with suitable spring force.

Situation "c": Called Oval Pad. It is easy to get the half ball with a serrated crown head.

We should use the suitable head tip for the Tin Spot, by and large, the pad size has a big gap. some pads only get 0.3~0.4mm( .0118~.0157''), nevertheless some other pads get over 0.5mm~0.8mm( .0196~.0314'').

Some advice for the tip head here you could definitely understand.

If it was a big pad like a 0.6mm( 24mil) pad, it is better to use a sharp probe, like a dagger head as the picture says. It can easily puncture into the flux pad.

#1: Cone Tip -30 degree sharp

#2: 3-Side Pyramid Tip - 30 degree sharp

#3: Sharp Dagger - 30 degree sharp

You will get a very good FPY( first passed yield), this will appear in not very very thin PCB board. So don't worry to have a try with some comparative sharp tips, they will help you a lot.

But will the sharp tip work for a small pad? like 0.3~0.4mm( .0118~.0157''). normally even the highest precision fixture makers are not able to avoid the fixture tolerance, so it is better to use multiple points head, it gets more percentage to get the soldering spot.

#4: 4-Point Crown

#5: 9-Point Serrated Crown

Note: Here we must make sure the tip gap never exceeding pad size. This can guarantee one of the pinpoints can get into soldering pad.

But for Gold finger pad, we could use the round head to get touching, some probe expert will suggest using the sharp head to contact directly so that ensure the high FPY when the PCB is not original material.

#6: Round Head, it can stop gold pad or fingers from footprints by the In-Circuit Test.

------------------------------------------Via Hole- Test Probe Tip Selection-----------------------------------------

Up is for Pad test, here we need have more comments about how to select a probe head tip for the via hole and dip in In-Circuit Test.

Actually, many ODM or OEM manufacturers deal with via holes in different processes, some industries they don't fill the Tin solder paste into the via holes when they have a good PCB print process. However, some others will do. So we will confront the two situations.

The top 3 via holes are not filled with soldering paste, so we can use the dagger or pyramid to cut into the copper ring, so the current can catch.

Top bottom 3 via holes are filled with soldering paste, so we can use 90-degree or 120-degree angle dagger to puncture the Tin paste, also can get the current going. But please don't use too sharp dagger or probe( like #4), this will damage the solder paste that wasn't the PCB manager want you to do.

It is easy to get it!!! just remember cutting the copper ring is the better choice.

------------------------------------------ Dip Feet- Test Probe Tip Selection--------------------------------------------

To test the dip feet, many people think we should use a CUP tip( #1) to catch the dip. It is absolutely wrong, the cup is always accumulating the flux, so after several times, cup gets full of flux. It can't work finally.

Optimized options are using the bladed crown( #2) or sharp point( #3). Of course, #3 head tip will bring a risk of board puncturing. so please take action seriously. About #2 you could use 6 bladed-crown, 7 bladed-crown, lotus head, it will keep a good FPY.

All above is about How to select a test probe head tip when you apply in In-Circuit Test. Wish it can help you a little bit.