Press-Fit Technology (2)

Press-Fit Technology

As a solder free fastening technology, press-fit technology frequently offers an attractive alternative to simple soldering technology. An effective electrical press-fit connection is created by pressing a pin into the plated through hole of a circuit board and – as part of cold welding process – generating a gas-tight electrical connection.

The trough-hole plating for a press-fit system is essentially made in the same way as are the holes for accepting components for THT soldering. Thus there are no changes required in the pcb manufacturing process. One outstanding characteristic of the press-fit system compared to the soldering system is that it produces not only an electrical connection but also an extraordinarily strong mechanical connection between the inserted components and the pcb.

Continuous and extremely homogenous material transition between press pin and through-hole plating.

With regards to long-term reliability, the press-fit system is convincing since it has the lowest FIT value (Failure in Time) of the overall system. It is up to 30 times better than that of an SMT solder joint. A single solid press pin has a typical extraction force of 100N or approximately 70% of the insertion force. Therefore press-fit connections are predestined to provide not only electrical but also mechanical connection solutions for electrical components.

If after press insertion a solid press pin in a 2.4 mm thick printed circuit board fits on each corner with more than 3° against the sleeve, the press connection zone has a lower electrical resistance than the brass pin itself and thus does not pose an electrical or thermal bottleneck. The connection surface angle is normally much greater, which provides a generous safety buffer for the electrical connection.

Advantages of the Press-Fit Technology

Very high ampacity, ideally suited for high continuous and peak currents
Press-fit connections show extremely high environmental stability
Low-resistance connection (< 200 µΩ) means low self heating, hence less heat must be dissipated through the system
No heat development on sensitive components and no thermal stress of the circuit board
Extremely stable mechanical
No problems with cold solder joints
High mechanical retaining forces
Double-sided mounting of circuit boards is possible
Much higher long-term reliability as for solder connections
More secure than soldering and screw connections
No changes in the production of circuit boards necessary

Using the Würth Elektronik power elements, currents of up to approx. 300A can be transferred to the printed circuit board. These power elements provide wide-ranging application options.


Press-fit element for currents of up to 160 A	Press-fit element for currents of up to 300 A	Press-fitting of power element: PCB with copper bar

DC power connection up to 120 A	Two-hole cable lug	Angled power element for connecting the assembly with the housing


Option for fitting a fuse	High current Board-to-Board connection

Processing

Press-fit system

The processing of press-fit elements fits seamlessly into the production process and is thus very cost-effective. Multiple power elements can be fitted simultaneously using press-fitt tools. Compared to soldering, the printed circuit boards are not subjected to thermal loads.

Other components should be spaced at least 4mm away from the press-fit hole
The hole should be at least 3mm away from the edge of the circuit board
No special tools are necessary for the pressing process. Simple lever press is usually sufficient
The insertion force per pin should be at least 40 N. Typically this force is around 150 N/pin
The press connection area must be supported during the pressing process
The press stroke should be 90° to the printed circuit board. The pins should protrude slightly from the printed circuit board after the pressing process
If two-part press-fit elements are used, the base part must always be fitted first to the printed circuit board
Press-in-process should be made after all soldering processes because of high heat absorption of power elements

If not stated otherwise in the drwaing, the Würth Elektronik power elements have quadratically designed press-fit pins. The through-hole plating in the PCB must therefore have the following characteristics:

Drill hole diameter 1.60 (-0.03) mm
Final hole diameter 1.45 (⁺ 0.05) mm for HAL
Final hole diameter 1.475 (⁺ 0.05) mm for chemical surfaces
Min. amount of copper in sleeve 25µm (optimal 30-40 µm)
Tin coating max. 15 µm (optimal 2 µm)

Our power elements are designed for the press-fit system. Alternative processing methods, such as soldering, are not contemplated.

Characteristics

Material:

Surface:

Retaining forces:

Insertion force:

Extraction force:

PCB thickness:

Force-fitting speed:

CuZn39Pb3

tin plated

as per IEC 352-5

Max. 250 N per pin,

min. 40 N per pin

Min. 30 N per pin

1.6-3.2 mm

100-250 mm/min

Via specification for chemical surfaces	Via specification for HAL

Power elements in Press-Fit Technology

Power Elements in Press-Fit Technology

Pins	Bushes with Two Rows Pin-Plate	Bushes with Circumference Pin-Plate	Bushes with Full Plain Pin-Plate	Shanks with Full Plain Pin-Plate	90° with Two Rows Pin-Plate	90° with Full Plain Pin-Plate	Two Part Power Elements, Ground Elements	Two Part Power Elements, Support Elements
4			M3					ᴓ 3.2 ᴓ 4.2 ᴓ 5.2 ᴓ 6.2 ᴓ 8.2 M3 M4 M5 M6 M8
6	M3				M3, ᴓ3.2
8	M4, M5, M6	M 2,5			M4, M5, ᴓ 4.2, ᴓ 5.2		ᴓ 5.5
9			M3	M4, M4, M5		M3, ᴓ 3.2
10	M8				M6, M8, ᴓ 6.2, ᴓ 8.2		ᴓ 7.3
12	M10	M4, M5					ᴓ 9.8, ᴓ 10.5
16		M6	M4, M5, M6	M5		M4, M5, ᴓ 4.2, ᴓ 5.2
20		M8, M10
25			M8	M6, M8		M6, M8, ᴓ 6.2
36			M10	M10		M10

Material: Brass (CuZn39Pb3)
Thread Size	M2.5	M3	M4	M5	M6	M8	M10
Torque (Nm)	0.29	0.5	1.2	2.2	3.9	9.0	17.0
* The Ultimate Torques can be taken from DIN 267, Part 25

Derating Measurement for Power Elements


* Operating current is defined by the PCB, cross section of the cable and cable lug. Suggested cross section according to VDE 0100 on page 153.

Get the AppNote as pdf version here