July, 2020

Page 53

Improving Yields with the Right Hand Soldering System Continued from page 50

Inductive vs. Resistive In inductive heating, the AC current flows

through a precisely wrapped electrical coil, creating an electromagnetic field, and the heater core material experiences eddy current losses in the magnetic field, which causes the core to heat.

In resistive, the heat is generated in the

heater coil wire and radiated to the core. Inductive heating has much lower thermal resistance, due to eliminating the need to radiate heat to the core and offers better per- formance. Originally, the difference in some tem-

perature specs between inductive and resis- tive designs were significant, especially when it came to temperature recovery times. Over the years, designs in resistive heating have improved. However, the differ- ence in recovery times between induc- tive and resistive systems on the mar- ket can still vary considerably. Operations managers report dif-

ferences that range from two to three seconds up to 10 or more seconds per joint, depending on the quality of the engineering of the particular solder- ing system, size of the joint, assigned temperature, geometry of the tip, and operator skill.

With a nod to the real estate mantra of “location, location and location,” the three key determining factors in

soldering performance can be said to be “temperature, temperature and temperature.”

For some operations, this extra

time may be of minimal consequence. However, for high-volume operations where throughput is the order of the day, the extra seconds expended for each joint — multiplied over several thousand PCBs per shift — can create an adverse condition of suboptimal throughput and yields. The best way to determine the

relative throughput of a resistive or inductive soldering system is to run a 10-load test, in which the operator creates 10 joints under identical con- ditions — same components, same tip, same temperature — except for using the respective soldering sta- tions, and then compare the results. Finally, when comparing induc-

tive and resistive soldering stations, it is also important to realize that rel- ative wattage, which is often a con- venient way to measure relative power among different devices in the same technology class, becomes unhelpful. Among resistive soldering sta-

tions, a 250W machine is undoubted- ly more powerful than a 180W machine. However, a 120W inductive machine might be more powerful than either resistive one.

Adjusting Temperature on the Fly The relative skill and experience

of the operator is a vital factor in the speed and quality of each solder joint. Most operations report having a mix of skill levels among their respective workforces. Most managers have noted that

their operators, when given the opportunity, will manually increase the soldering temperature of their system to above the specification in order to meet their quotas. This

Comparison of resistive heating and inductive heating.

might be especially true if they are using an under- performing system, where a few seconds of extra dwell time can potentially cause a frustrating slowdown. The danger is that adjusting the temperature

outside of the spec determined by engineering experts and component manufacturers can lead to damaged components and delaminated boards. When caught in inspection or test, this can lead to scrap boards and components or the need for cost- ly rework. Many manufacturers believe that sol-

dering temperature should be 100 percent controlled by management and the predeter- mined engineering spec, rather than allow- ing individual operators to adjust the tem- perature on the fly, as is the case with adjustable temperature systems. The introduction of inductive heating

systems provided a fixed temperature solu- tion, where the temperature range is deter- mined by the tip provided and “locked in” for the course of the workflow.

Continued on next page

See at SEMICON West (Virtual)

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