At the
same time, the requirements for the product’s reliability and life expectation
are continuously increasing, especially for high frequency (RF)
aqueous cleaning systems centered
technologies4. This in turn, makes cleaning a mandatory aqueous
cleaning system step and the
question as to which cleaning process can provide for the required cleanliness
levels under low standoff components (i.e. capillary spaces) has to be
addressed. Additionally, the contacts that are commonly found under components
such as BGAs, micro-BGAs or CSPs pose mechanical barriers and Axarel complicate the
situation further. Consequently, the capillary penetration of the cleaning and
rinsing agent is hampered. As a result, the number of additional requirements
for the cleaning step increases almost exponentially. A suitable semi aqueous cleaning
process should not only allow the cleaning media ample access to capillary
spaces, but it also has to lift off the residues, remove the latter from under
the respective components and most importantly guarantee that recontamination is
avoided as shown in figure 2. Figure 2. Mechanisms for cleaning/rinsing/drying
Even up to this day a common notion exits, which implies that traditional spray and immersion based processes, employing water- and/or solvent based Axarel cleaning agents, are only conditionally effective. Apart from the traditional mechanical assistance through semi aqueous cleaning ultrasound, spray-under-immersion aqueous cleaning systems and spray in air this view prompted the development of equipment processes that rely on centrifugal, high-pressure, vacuum and vapor phase support.
This study was conducted to provide process solutions for optimized cleaning under low standoff components. Various cleaning agents and mechanical process technologies aqueous cleaning system were evaluated based on their ability to clean efficiently. A specifically developed standardized testing procedure provided the basis for a comparable and objective overall evaluation.
Somewhat surprisingly, it was determined that the results obtained using the traditional processes mentioned above, were not significantly different to the ones obtained by using the newer, alternative mechanical methods. The main prerequisite for these findings was the ability that the contaminations (i.e. fluxes and solder paste) were generally cleanable with the cleaning agents used. In other words, for Axarel a given chemical compatibility between the contamination and cleaning agent used, the mechanical assistance played a aqueous cleaning system rather aqueous cleaning systems less significant role. Special test substrates were semi aqueous cleaning prepared for this study to simulate low standoffs. As worst case scenario a minimal standoff of 2 MIL (0.002 inches) was used as shown in figure. As part of the preparation and to effectively simulate the influence of mechanical barriers of BGA-type connections, glass coupons were placed and soldered on top of bumped CSP contact pattern, to which flux had previously been applied as aqueous cleaning systems shown in figure 4.
Ultrasonic cleaning cleaning solvent pcb cleaning aqueous cleaning ultrasonic cleaning systems aqueous cleaning systems flux residue flux residues Dr. Ok. Wack Ultrasonic cleaning equipment Ultrasonic cleaning system