In the 80's and 90's traditional Singaporean SME's (Small and Medium Enterprises) were highly dependent upon their large OEMs customers. After declaring its independence in 1965, Singapore, which had no natural resources, chose to turn to foreign companies as vehicles to achieve industrial growth and create jobs. The government of Lee Kuan Yew provided industrial infrastructure, peaceful employer-employee relations, a well educated workforce, low taxes and a logistic hub.
Hawker centers are a unique specialty of Singapore. They are large open areas with a wide variety of small stalls selling affordable cooked food. Many of my Singaporeans friends hardly cook at home as they enjoy walking down to the hawker center at dinner time. Besides offering affordable and diverse dishes, hawker centers also serve as a social link between the multicultural communities of Singapore.
In the manufacturing of Printed Circuit Board, through hole plating remains a complex operation. It involves wet chemical processes including deposition of metals by metallization and electroplating techniques. Although direct metallization has contributed to reduce the number of steps and chemicals involved in the process, it is still the source of a lot of anguish among the engineering community.
In the PCB industries, electronics soldering involves high temperature 250°C melting a soldering filler material, then making joints between the surface mount components & the board.
In the 1980’s SMT (Surface Mounted Technology) became very popular and eventually replaced the very reliable through hole soldering technique. SMT components either had smaller leads, or no leads at all which allow them to be smaller. Simultaneously by eliminating component holes in the bare PCB, designers were given more real estate and boards became smaller and high density.
2. From high temperature solder to low temperature conductive epoxy
The use of high temperature resistant bare board substrate (i.e. very expensive) is more driven by the soldering process than by the application conditions. In both wave soldering and oven reflow processes the temperature rises above 200degC.
In Flexible Printed Electronic, process engineers have replaced the high temperature solder with low temperature conductive epoxy which allowed low temperature material as PET (Mylar) to be used as alternative to expensive Polyimide (Kapton).
A decade ago CMI has developed a unique low temp SMT component assembly process composed of 6 phases.
- Chip bonder dispensing
- Conductive epoxy dispensing
- Pick and place
- Thermal curing
- Thermal curing
After much reflection and considering the medium-volume-high-mix market it was finally decided to start with dispensing and not screen-printing for the supply of the conductive epoxy and the chip bonder.
Pick-and-place is done using a Juki machine and thermal curing is achieved at 65degC.
Mechanical bonding is enhanced by the subsequent “encapsulation” process and the final thermal curing at 65degC.
In summary, the chip bonder holds the components firmly while conductive epoxy ensures good electrical conductivity between the components and the printed circuit. The encapsulant is here to enhance the mechanical bonding and provide a weathering protection.
3. Dispensing main parameters
Dispensing is at the centre of the assembly process and CMI has identified 7 parameters to be tightly controlled:
- Dispensing time
- Syringe pressure
- Retracting height
- Retracting speed
- Needle clearance distance
- Material viscosity
- Substrate flatness
The dispensing time and the syringe pressure will together dictate the volume of material to be dispensed.
One of the most undesirable effect is called “tailing”. It is the result of height and speed of the retract phase but also the needle clearance distance.
Finally, the volume consistency will be greatly affected by the material viscosity and substrate flatness.
Over the years automated programmable dispensing has proven to be a reliable process. Good process control is guaranteeing volume consistency and repeatability.
Without the need for tooling, digital dispensing allows CMI to respond faster to customer demand and to accommodate smaller quantities without increasing NRE (Non-Refundable Expenses).
I am old enough to remember the time when components had long leads and PCB had holes other than these tiny via holes. It was a time when components were mounted on a bare PCB by inserting the component leads into holes that were drilled on the PCB and soldered to pads situated on the opposite side.