A need for Innovation and Development
EDITOR ’ S CHOICE SELECTIVE SOLDERING
PILLARHOUSE INTERNATIONAL
A need for Innovation and Development
Selective soldering typically uses a wettable nozzle to apply solder to the underside of PCBs . This methodology allows the process to be tailored for specific joints and allows multiple nozzle types to be used on the circuit board . Controlled application of the solder is achieved by wetting ( adhesion ) of the solder to the nozzle .
Wettability is the study of the adhesion of liquids to solids as a result of the surface energy of the solid and the surface tension of the liquid . Generally , wettability is characterised by observing the contact angle of a stationary ( sessile ) droplet . In soldering , flux serves to clean the interface between the solder and nozzle and remove oxides that may impede the wetting process . After cleaning , a chemical reaction between the solder and nozzle determines the extent of the wetting but this interaction also limits the lifetime of the nozzle . It causes wear of the nozzle as the metal is leached into the solder bath .
A good nozzle must have good wettability to maintain a controlled process as well as balance the wettability and wear of the nozzle . Material composition must be carefully controlled to achieve this . A new nozzle material will reduce operation and maintenance costs for manufacturers by reducing the number of nozzles required overall and reducing downtime caused by nozzle failure . Improving the wettability of nozzles will allow for more challenging joints to be tackled using the selective method . This project has been undertaken due to customer requests to increase nozzle lifetime and reduce the maintenance required .
There has been limited development of improved selective soldering nozzles . This is due to the electronics industry being conservative in many respects and rightly so ; “ why fix what isn ’ t broken ” especially when reliability is paramount . However , there has been some research carried out on the application of surface treatments for extending nozzle life .
A good nozzle must have good wettability to maintain a controlled process as well as balance the wettability and wear of the nozzle .
This ground-breaking research project , part funded by Innovate UK and Pillarhouse International Ltd . is partnered with Coventry University through a knowledge transfer partnership scheme . The aim is to develop a new , longerlasting nozzle with excellent wetting properties . By applying the studies of tribology and materials science , fundamental work looking at different materials and surface engineering techniques has selected a number of potential candidates that show improved performance .
Prototype testing has been used to confirm compatibility with existing solders and fluxes . The new AP Master Nozzle will be available in June of 2023 .
For further information , please visit www . pillarhouse . co . uk
24 PECM Issue 62