How to effectively select a test probe head type?

electronics manufacturers

In a typical ICT test case, there are three main test solutions: solder joints, vias and pins. In-circuit testing and functional testing are offered by a number of electronic manufacturing service providers. Before we start discussing how to effectively select a probe head type, please have a preliminary understanding of our test environment.

Most electronics manufacturers have specific requirements and patents for their printed circuit board processes. Typically, however, after SMT, when the solder joints are formed, the rosin flows out to the outside of the solder joints as it cools at high temperatures, and then cures and covers the surface of the solder joints, making the rosin hard and resistant to puncturing.

Solder Joints - Test Probe Head Type Selection

Case a: Flat solder joints, which are easy to test because of the uniform rosin coverage.

Case b: Oval solder joints, which are relatively less easy to test because the rosin remains on the surface of the joint and requires the use of a probe tip type with the appropriate elasticity.

Case c: Goose egg shaped solder joints, relatively easy to test, rosin will be heavily concentrated at the root of the solder joint, only need to use a multi-clawed probe needle type.

We should choose the appropriate probe tip type for testing according to the size and pitch of the solder joint. Some solder joints are only 0.3-0.4mm in size, while others are between 0.5-0.8mm.

The following are probe tip options for testing solder joints:

1. If the size of the solder joint is similar to a 0.4mm (24 mil) solder joint, it is best to choose a needle type with strong piercing properties, such as double sided knifing needles, conical and triple tapered.

- Conical - 30 degree point

- Triple Tapered - 30 Degree Point

- Sharp Knife Sharp - 30 Degree Sharp

2.Excellent first pass rates (commonly known as straight-through rates) can be achieved with these types of header patterns, and they are typically used on thicker PCBs to ensure that zapping does not occur.

3.However, are these sharp tip types suitable for small solder joints? As with 0.3-0.4mm sized solder joints, it is not easy for even precision fixturers to choose a probe needle pattern that is too sharp because the fixtures also have off-set tolerances. Therefore, the best way is to use more claw shaped needles for testing, which can better ensure the percentage of contact solder joints.

4. four-jawed crown type

5. 9-jaw tooth type

Note: We must make sure that the spacing between the teeth does not exceed the size of the solder joint, which ensures that at least one of the needle points can contact the solder joint.

For gold finger pads, we can use the round tip type for contact. Some probe experts recommend using a pointed needle to contact the solder joint to ensure a high throughput rate.

6. round tip, which ensures that the gold finger leaves no trace.

Through-hole - Test Probe Tip Selection

Next, we discuss how to test vias.

Many electronics manufacturers use a variety of processes for vias on PCBs. Some are direct through-hole fabrication processes, while others are filled with some solder paste to increase the likelihood of through-hole conduction. However, this process of adding solder may result in tin flattening and tin popping.

As shown in Figures 1, 2 and 3, these three are the test probe needle types when dealing with through holes. It can be used double-sided knife cutting needle or three-sided cone.

But if you increase the solder paste process, as shown in Figure 4, 5 and 6, the use of too sharp needle will pierce the solder paste, destroying the original increase in solder paste conductivity of the original intention, so it is not desirable. The latter two needle type for testing is better, but also better use of the blade to cut through the copper ring contact, while increasing the possibility of the tip of the needle into the solder paste, to ensure that the straight-through rate, but will not damage the solder paste.

Pins - Test Probe Tip Selection

In order to test pins, many people believe that the approach in Figure 1 should be used. While this method is convenient for accessing the pins, due to rosin and spoilage, after a few contacts the pins are

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