Ceramic Chip Resistors & Caps & the Hot Air Pencil. As the transition from Thru-Hole to SMT accelerated, an immediate drawback with the use of soldering irons and hot tweezers appeared: miniature ceramic chip capacitors and resistors cracked or fissured when soldered to the PCB. The cracking problem rose up from the severely unequal expansion rate between the ceramic chip and its leads created by contact soldering irons. Thus, pin-pointed hot air soldering became the favored method. But how best to do it?

In 1994, Randy Walston and I introduced the first true hot air pencil to the soldering market to great fanfare at the NEPCON West Electronic Exposition in Anaheim, California. In fairness, there had been other hand-held hot air soldering tools on the market, but they were either large in diameter, bulky, awkward to hold, blocked the vision of a technician from the chips to be soldered, powered by high voltages where transient leaks and switching voltage spikes put noise into the power lines (and damage SMD's if touched), or were re-packaged hot air "tools" inside of existing soldering iron handles. The patented AirPencil™ design stole the show attended by nearly 40,000 engineers, technicians, designers, manufacturers and quality personnel. Over 2,000 written inquiries to the show's administrators were submitted.

Today, most every manufacturer of ceramic capacitors and glass diodes have published papers and warnings that they are not responsible for damage done to their ceramic caps induced by hand soldering irons because of the above stated problems and state that soldering irons are prohibited as soldering tools with their devices.

Yes, one could remove a chip quickly with a heated contact tool (soldering iron or hot tweezers), but once removed, the chip could not be re-used.

Cracking & Fissuring: More importantly, soldering new ceramic chip capacitors and resistors with contact type tools became prohibited by many prestigious electronic firms to prevent  chip cracking/fissuring. Instead of the soldering iron and hot tweezers, the hot air pencil quickly became the preferred tool for soldering ceramic chip SMD's. Moreover, the hot air pencil proved most effective in the removal of chip capacitors, chip resistors, and SOIC's when utilized with (non-heated) tweezers.

Also, hot air pencils, not soldering irons, became preferential preparing or "touching up" pads. Soldering irons can leave tags or ice cycles on the pad causing co-planarity problems at the lead/pad interface. A hot air pencil leaves a smooth pad. This process is now known as hot air leveling.

More Advantages of Non-Contact Soldering: The beneficial applications of the hot air pencil quickly transcended  more than just ceramic chip caps, resistors, and SOIC's. The hot air pencil quickly proved to be superior for soldering of a newer type of SMD: fine and ultra-fine pitch devices (FPT & UFPT).

Between 1988 and 1995, demand by designers for higher I/0 counts on IC's pushed electronic packages to extremes. Earlier SMD's had lead counts at 100 or less with pitch spacings typically between 0.040" and 0.050", but newer FPT and UFPT chips had I/O counts as high as 250 plus. Complicating things further, these devices had pitches as small as 0.015".

In 2004, NASA heralded the "touch-free, precision soldering method" of the patented Zephyrtronics AirPencil™ in a 104-page report recognizing the aforementioned attributes of pin-pointed hot air for PCB tasks. "Touch-free." Perfectly said.

Limitations of Hot Contact Tools and QFP's. Where hot contact soldering irons, hot bars, and hot tweezers were inadequate for the placement of ceramic chip capacitors and resistors, the limit of their usefulness became more apparent with the arrival of these ultra fine pitch components like Quad Flat Packs (QFP's).  Chip miniaturization also translated into tinier leads, too.

In fact, the component's leads spotlighted the disadvantage of soldering irons when compared to the non-contact (hot air) method. The leads became so delicate, so small in overall footprint (width, thickness, and even extension of the toe) that they proportionately became extremely susceptible to bending, twisting out of their axis and deforming whenever touched by a contact type tool.