Rigid needle adapter
Rigid needle adapters are used to test electronic assemblies. With their thin rigid needles, they enable the contacting of finer structures on assembled and unpopulated circuit boards than is possible with a conventional adapter with spring pins . Furthermore, rigid needle adapters also enable high- pole micro- plugs to be contacted in that the adapter is guided into the connector via the housing and the rigid needles contact the connector there.
construction
In the rigid needle adapter, rigid needles guided in several adapter plates are deflected from the grid head to a contact point (test pad). When making contact, the adapter is compressed by this contacting stroke at a certain adapter height. The rigid needles are pressed into the corresponding spring pins (pogo pins) in the grid head by this stroke , whereby the contacting force is built up. They can be deflected by 2 to 3 mm via these guide plates, which means that contact pitches down to 80 µm can be made on the test object.
A spring contact pin is embedded in the grid head for each test point . These spring pins are arranged in a grid (this is where the name comes from) so that the greatest possible test density can be achieved. Fine grid heads can have a 0.6 mm grid of up to 280 spring pins / cm². With a contact stroke of around 2.5 mm, forces of 0.4 N to 1.5 N act per contact point, depending on the spring pin.
The rigid needles running obliquely in the adapter can also be deflected so that they emerge vertically from the adapter. This technology minimizes the wobble play of the rigid needle and it is possible to contact smaller test points and closer to electronic components . With this adapter design, 0.5 mm can be positioned next to the rigid needles also hold-down devices in order to optimally support the test object when contacting on both sides.
Service life of rigid needle adapters
The contacting tip of the rigid needles is flattened over time as a result of the contact. The service life depends primarily on the material to be contacted and the test force used by the spring pin. Around 500,000 contacts are achieved under optimal conditions.
The spring pins embedded in the grid head are protected from greater transverse forces and contamination and thus have a service life of well over a million contact cycles.
Combination of the finest spring pencils and rigid needles
The combination of spring pins and rigid needles are selected according to the requirements.
Rigid needle adapters for very fine structures are also known as micro adapters ( Micro Contacting Adapters , MCA). The table on the right shows as an example which spring pins can be combined with which rigid needles in microadapters. One tries to use rigid needles that are as thick as possible, as these are more stable. The selection of the largest possible rigid needle diameter is primarily determined by the existing contact distances.
The maximum current that can be transmitted is usually limited by the spring pin or the contact transition from the needle to the test item. It is defined by the measuring power (P = I² × R) in the spring pins and in the rigid needles. If the currents are too high, the rigid needles and spring pins can get hot and damage the test item and the adapter. The values given in the following table come from laboratory tests and provide guide values.
- Permissible currents:
Continuous current (ID) and pulse current (II) at 10 ms:
- A: ID = 0.2 A / II = 0.4 A
- B: ID = 0.3 A / II = 0.9 A
- C: ID = 0.6 A / II = 1.8 A
- D: ID = 1.0 A / II = 3.0 A
- E: ID = 2.0 A / II = 6.0 A
- F: ID = 3.0 A / II = 9.0 A
- Permissible stresses:
The possible test voltage can only be roughly calculated, since the influence of air humidity plays a major role here. A rule of thumb says: a voltage of 1000 volts requires a distance of about 1 mm. With this rule of thumb, the following formula can be established for the needle distances:
- Maximum voltage = 1000 volts / mm × (pitch - needle diameter)
Example: A pitch of 0.2 mm is contacted with a needle diameter of 0.13 mm. The maximum test voltage is then: 1000 volts / mm × (0.2 mm - 0.13 mm) = 70 volts
Testing with the rigid needle adapter
Circuit boards are contacted at different times so that the quality of the individual process steps can be checked. The unequipped circuit boards are usually checked for short circuits and interruptions so that later circuit boards that are not defective can be equipped with expensive components. After assembling the circuit boards, the components are programmed during flashing and checked with the in-circuit test. Finally, the complete function of the circuit is checked during the function test. By using a rigid needle adapter for these tests, the required test area can be reduced to a minimum, thus minimizing manufacturing costs.
Contacting bare circuit boards
In the case of bare circuit boards, the adapter can be positioned close to the test item so that the rigid needles only protrude minimally from the adapter. This reduces the wobble play (tolerance play of the rigid needle at the test point) and enables smaller test points and test intervals. The smallest possible pitch is therefore mainly dependent on the rigid needle thickness and starts at 80 µm.
Contacting assembled circuit boards
With assembled circuit boards, the component height is overcome with the rigid needle exit. The exit length influences the required thickness and the wobble clearance of the rigid needle. Parameters for contacting assembled substrates with a rigid needle adapter:
- Needle exit 0 mm - 2 mm enables testing on 0.10 mm test structures with a pitch of 0.25 mm
- Needle exit 2 mm - 4 mm enables testing on 0.12 mm test structures with a pitch of 0.40 mm
- Needle exit 4 mm - 6 mm enables testing on 0.15 mm test structures with a pitch of 0.40 mm
Higher components are cut out in the adapter so that the distance from adapter to circuit board can be realized as closely as possible.
By reducing the test point size from e.g. B. 0.8 mm to 0.2 mm, the actual test area can be reduced by 16 times. In addition, the test points can be set more easily when layouting, so that additional test points can even be set.
Double-sided contact of printed circuit boards
With the rigid needle adapter, contact is made in two strokes. With the infeed stroke, the adapter with the hold-downs is moved towards the circuit board so that the circuit board is optimally supported. The contacting stroke is then implemented, during which the test force is applied from the spring contact pins to the circuit board via the rigid needles. This regulated sequence means that the circuit board is contacted as gently as possible.
As a comparison, with a conventional adapter, the spring contact pins exert almost their full contacting force before the hold-down devices can even support the circuit board. In this short state, this leads to severe deformation and thus to greater loads on the circuit board.
Possible uses of rigid needle adapters
As a result of miniaturization, the conductor tracks on circuit boards are becoming increasingly narrow. They can then often no longer be contacted with conventional spring pin adapters. Rigid needle adapters can be used in the following ways:
With vacuum adapter
Compact rigid needle adapters can be integrated into a vacuum adapter . The vacuum is used for the stroke, the test item itself is in a vacuum-free zone. The adapters can be expanded on one or both sides and also as 2-stage contacts for separate in-circuit tests and functional tests .
Properties:
- Contact on microvias , test pads, micro plugs
- Single and double-sided contact
- Contact pad> 400 µm (when centering via catch pins)
- Up to 100 test points / cm² with a 1 mm grid
Production lines
Rigid needle adapters are used in semiautomatic and fully automatic handling systems for testing unassembled and assembled printed circuit boards. The contact pitch is <0.4 mm.
Properties:
- Contact on microvias, test pads, micro plugs
- Single and double-sided contact
- Contact pad> 70 µm (with optical centering)
- Contact pad> 300 µm (without optical centering)
- Up to 280 test points / cm² (with a 0.6 mm grid)
Chip adapter
Rigid needle adapter can (optionally in combination with conventional adapter technology) already equipped IC 's lontaktieren.
Properties:
- Contact on test pads
- Single and double-sided contact
- Contact pad> 250 µm
- Contact pitch> 400 µm
- Up to 280 test points / cm²
Use as a plug adapter
When making contact with small connectors on circuit carriers, the adapter is usually guided via the connector housing, which eliminates the tolerances of the carrier and assembly. The advantage is that the smallest connectors can be contacted directly and the contacts do not have to be picked up via a mating connector, which often has to be replaced after 20 to 30 mating cycles.
Properties:
- Contact directly on the plug contacts
- Single and double-sided contact
- Connector contact width> 150 µm
- Up to 200 test points / cm²
- Pneumatic stroke release
Use in the laser trimmer
The rigid needle adapter can also be used in the laser trimmer . The adapter moves under the substrate and supports it from below. A seal is pressed onto the substrate from above and the necessary counterpressure is then built up in the pressure chamber for the rigid needles. If this counter pressure is present, the adapter on the component side can contact all measuring points at once. Through the pressure chamber, all resistors within the pressure chamber can be contacted at the same time, which makes laser trimming more efficient.
Properties:
- simultaneous contacting of all measuring points
- Trimming of all resistors without repositioning the contacts
- Contact pad> 70 µm
- Contact pitch> 150 µm
- Up to 280 test points / cm²
Staggering
The aim of staggering is to be able to test the finest structures with the thickest possible rigid needles. In staggering, the contact points are offset from one another on the circuit boards so that they are as far apart as possible. According to the Pythagorean theorem, a relatively small distance A (distance between contact points) can be achieved with a large distance C (thickness of the needles and insulation distance). The pitch that can be realized in such an application is made up of the distances A and B outlined :
If you use this staggering with a fine pitch, you can contact the following distances:
- Rigid needle diameter 0.04 mm → Pitch from 0.08 mm
- Rigid needle diameter 0.07 mm → Pitch from 0.12 mm
- Rigid needle diameter 0.10 mm → Pitch from 0.15 mm
- Rigid needle diameter 0.13 mm → Pitch from 0.20 mm
- Rigid needle diameter 0.18 mm → pitch from 0.25 mm
- Rigid needle diameter 0.30 mm → Pitch from 0.40 mm
- Rigid needle diameter 0.45 mm → Pitch from 0.55 mm
- Rigid needle diameter 0.60 mm → Pitch from 0.70 mm