Press_fit_technology_overview

Press fit technology

Press fit technology – as one of the most important manufacturing technologies – has become well established in production processes of the electronic industry. Based on the norm IEC 60352-5 press fit technology is recorded and appraised in a qualitative manner.(定性方式)

Press fit technology is based on the fundamental method of pressing a contact pin (with or without an elastic press fit zone) using pressure in a metalized borehole(金属化孔), or as the case may be, a feed through(连通). Due to the extensive range of the contact pin and the smaller bore diameter of the metalized borehole, Press fit technology – as one of the most important manufacturing technologies – has become well established in production processes of the electronic industry. It results in a gas proof(气密), electric conductible connection(导电连接). On suitable surfaces we talk about a cold shut and so an inter metallic connection. The above named Norm indicates the important values for the transfer resistance, that also prior to specified checks (vibration(振动), harmful gas(有害气体) and temperature stress test(温度应力测试)) must not deviate from the specified limit value. The definition of the maximum press fit technology and holding power of the contacts is specified by the connector manufacturers in press fit technology. This is particularly based on the fact that different designs in the press fit zones and the used materials and surfaces can lead to wide scattering.

The press fit technology offers many advantages. The most important are:

- Cost reduction

- Reduced down-time(故障时间) in production

- Higher processing speed

- Reparability and simple recycling

- And a high reliability and process safety with a constant excellence

In detail this is achieved by the press fit’s own factors:

- No additional thermal strain(热应变) on the PCB

- No additional cleaning processes

- Minimal down-times

In addition new connector systems can be used: –feed through connector systems comprise of connectors with long posts and shrouds(长柱和外壳) that are pushed on on the opposite side. - Wire-Wrap connectors(电线缠绕连接器) (for direct point to

point wiring connection as a backplane- replacement/extension).

Pic. 1: Wire-Wrap-connection and shroud application

Pic. 2: Shroud

These systems are not feasible in solder technology, as wave soldering results in bridging on the long contact posts.

In recent years, time and again experiments（时间和实践）have been carried out with various press fit zones in press fit technology. For a long time every manufacturer of connectors developed their own press fit zone, advertised it’s advantages and so attempted to ensure their market share. However with increasing pricing pressure only a few press fit zones established themselves. Today next to the fixed press fit zones still used for high voltage applications there are only four press fit zones with an elastic press fit zone:

- Needle-Eye

- V-Shape (V-Zone)

- …Action-pin“

- …Tcom“

contrary to the fixed press fit zones, the necessary press force with flexible press fit zones is transferred evenly to the backplane. Thereby greatly reducing the mechanical stress on the backplane. Warped PCBs and torn through-plating are a thing of the past.

Pic. 4: Fixed and flexible press fit zone in acticomparison

For press fit technology qualification, as well as limit values for the contact resistance (<1 mΩ), the press fit force and the holding force of various end conditions can be used. The tests and their results allow a direct or indirect conclusion on the excellence of the process and therewith also the quality of the press fit connection..

Pic. 5: Measurable values and the practicability of the measurement

To sustain the stability of the manufacturing process however only one part of the measurement is feasible.

It has been shown that many factors have a direct effect on the press fit force. It is therefore possible, with relatively simple press fit force measurement methods, to sustain the process on a stable level to be able to intervene immediately when deviations occur.

Pic. 6: The most significant factors on the press fit force

During the press fit process two metalized surfaces rub together. The surface finish (表面加工)and the material used determine the press fit force.

Thereby the metallization and the layer composition of the through-plating bore(通孔) is relevant. The bore structure(孔结构) is controlled via standards by the connector manufacturer

For connectors of the series DIN 41612 the guidelines are valid according to IEC 60603-2 and IEC 61076-4-100:

Contrary to tin and lead coated backplanes, for all other surfaces a measurement of more than 1 mm must be achieved for the plated through hole. Primarily nickel. Tin or gold are used for connectors. The various plating on the backplane sides can result in enormous fluctuations in press fit forces.

Pic. 8: Press fit force for a single contact in various surfaces

Admittedly, the holding force of the copper casing in the backplane is only limiting factor in order to avoid too high press fit forces that can lead to problems.

Pic. 9: Jet- or nozzle effect when press fitting

These problems can only be countered when the above named guidelines for the backplane are complied with and the connector manufacturer reliably controls the manufacturing process.

Specifically because of the simple and cost effective manufacture - surfaces with chemical tin are used. Manufacturers in the USA use backplanes with chemical silver because of the better process ability in the Reflow-soldering process.

Conclusion

The direct process factor “ press fit force” allows us to draw conclusions on almost all of the influencing variables. Also without additional backplane parameter measurements, (hole diameter, backplane thickness etc.) a constant manufacturing process quality can be guaranteed. For this reason it is imperative – if a fault occurs –to implement a measurement and an automatic shut-down. There are many proposals, however, most of them require additional measurement data regarding the used backplanes or connectors. By contrast HARTING offers a press fit automat that

independently calculates the necessary parameters from the press fit data. The latest development the CPM prestige possesses very accurate data logging and the universal shut off log autosense. Thereby the press fit machine that possesses easy to use software and a touch monitor as input interface is pre-destined for every user area. The maximum press fit force of 199kN allow backplanes and daughter cards to be processed safely.