Air Pencil, Hot Air Pencil, SMD Soldering, Hot Air Soldering, Ceramic Capacitor, Cracking, Thermal Shock
How To Solder Tiny
SMD Chips With a
 Hot Air Pencil

 
 Hot Air Soldering   Hot Air Pencil    SMD Rework    PCB Repair   Non-Contact   Touch-Free Soldering for Ceramic Caps  
[TECH 1] [TECH 2] [TECH 3] [TECH 4] [TECH 5] [TECH 6]
History & Theory of Operation:
Hot Air Pencil, Soldering
A Hot Air Pencil Should Be "Pencil" Thin To Provide Chip Visibility 
   
THE HOT AIRPENCIL
Copyright © 1996, 2008, 2009, 2010, 2011 and 2012 by David Jacks


Zephyrtronics Equipment is Designed, Engineered, and Manufactured in the United States of America.


 


 


 


 











 

 
OVERVIEW:    

Hot Air Soldering, Precision, Pin-Point, Reflow Soldering, Air Pencil
A Hot AirPencil is Shown Above Used In Concert With a Bottom-Side Preheating AirBath.

The introduction of the hot air pencil as a soldering device for surface mount devices for high quality soldering reflow on PCB's at a bench --- whether in prototype, design or rework/repair ---  along with bottom-side PCB preheating seems obvious now, but it it was not always so.

The hot air pencil made its entry into the PCB production world in the 1990's  almost 10 years after the advent of surface mounted technology.

Together, the AirPencil™ with preheating proved that it was then possible to mimic the initial production soldering thermal profiles, processes and equipment.

 

Even the briefest study of any state-of-the-art, high volume PCB production process --- along with the most basic semiconductor data books --- will emphasize how  precise handling methodologies and exacting solder reflow prerequisites are essential for many very critical quality reasons.

And since it only logically follows that all PCB tasks performed at a benchtop should be held to the same equal standard of high-volume production, some fundamental conclusions can be made as just how to achieve premium solder joints at the bench:

 
  • All PCB's should be carefully thermally ramped 2ºC-4ºC per second with a preheating “soak” prior to soldering or desoldering tasks whether in production, prototyping or in rework or repair.
     
  • Non-contact and non-contaminating hot air soldering (convection) is best suited for ceramic chip resistors and capacitors.
     
  • Non-contact and non-contaminating hot air soldering (convection) is best suited for placement of fine pitch and ultra-fine pitch semi-conductors.
     
  • When hot air is used to remove or replace SMD's, the air-stream must be pin-pointed precisely to the targeted leads and pads with a  hot air pencil  or with extra-low velocity hot air nozzles  if with a larger SMD/BGA Hot Air Benchtop system.
 
  • Components adjacent to an SMD that is being removed or replaced should never be exposed to elevated reflow temperatures.
     
  • PC boards and their components should never be subjected to temperatures greater than originally seen during initial production reflow.
     
  • An accelerated cool down of the solder joint is desirable and recommended to insure robust joints and to prevent accidental skewing, misalignment, and/or tomb-stoning.
     
  • Static-sensitive electronic components should be protected during printed circuit board assembly rework from accidental static discharges. And the use of an ESD wrist strap by the rework engineer or technician is recommended.
 

Air Pencil, PLCC, QFN, SMD, SMT, Hot Air, Soldering
The Hot AirPencil is Shown Above Soldering a Quad Flat Pack (QFP). Notice the 100% Non-Contact of the AirPencilto Delicate Leads.

A BRIEF HISTORY: CONVECTIVE vs CONDUCTIVE REFLOW:  Reflow soldering has generally been divided into two soldering processes: convection and conduction. However, with the advent of SMD's and miniaturization of chips, the physical contact required during conductive soldering quickly lost favor with manufacturing and quality engineers. High volume conveyor ovens and hot air equipment (convective) quickly became preferred over the traditional contact methods (conductive) such as soldering irons, hot bars, thermodes and even wave soldering (also contact).

 

Creating electrically sound and physically robust solder joints -- between a chip's leads and its tinned copper pads -- requires attention to many process parameters. Within even the most nominal PCB assembly, a host of dissimilar materials can be found: copper, fiberboard, ceramic, plastic, tin, lead, silicone, laminates, and more. Each of these distinct materials have varying thermal expansion rates. If ignored during exposure to solder reflow temperatures, many compounding problems.

 

 

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.


Video: How To Use Solder Paste?

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.

Air Pencil, PLCC, QFN, SMD, SMT, Hot Air, Soldering
The Hot AirPencil is Shown Above Soldering a PLCC Package. Notice the 100% Non-Contact of the AirPencil to the Delicate Leads.

     
         

Advantages of Hot Air Pencil Over Hot Contact Tools. An AirPencil™ hot air  never "touches" the component or its tiny, fragile, and weak leads. The opposite is true of the hot contact reflow tools where the tool can "stick" to SMD leads, bend SMD leads upwards/downwards causing co-planarity problems, tweak SMD outwards/ inwards causing electrical shorts or opens. The AirPencil™ pencil presents none of these problems. It allows no opportunity for introducing contamination to the PCB as opposed to the hot contact tools. Dirt, grime, residual flux and adhesives can and often stick to contact tools cross-contaminating  PCB...and creating even more quality problems.

 

Plus, the AirPencil™ can be used to gently pre-heat the surrounding area of a targeted chip before soldering or desoldering so lower temperature settings and shorter reflow dwell times can be achieved. Of course, the preferred and most quality-effective, auxiliary compliment to the hot AirPencil™ is a temperature-controlled, bottom-side, forced-convection preheating system. Such a mild pre-heating of the PCB right at the bench can really be of great assistance when processing PCBA's with heavy ground planes, multi-layers, or large heat sinks.  -- David Jacks, 1996 Los Angeles, California

 

Soldering, Ceramic Capacitors, Hot Air Penci, Soldering Paste
Ceramic Capacitors Must Be Reflowed With a Hot AirPencil Instead of a Contact-Style Soldering Iron Which Fracture and Crack the Chips.

  *********************    

ABOUT THE AUTHOR: David Jacks was Director of Engineering with the two largest soldering equipment manufacturers in the world for 14 years before founding the Zephyrtronics company in 1994 with his business partner, fellow engineer Randy Walston.

David's professional design career as an inventor stretches from the early 1970's in Los Angeles.

 

His designed products have been spotlighted in feature articles in both Popular Science® and Popular Mechanics® magazines.

He has designed products, tools and appliances marketed by Sears®, Black & Decker®, RadioShack®, Motorola®, Snap-On Tools®, Rubbermaid®, CooperTools®, Farmer Brothers® and Brewmatic®.

 

David holds multiple patents (utility and design) for his many inventions; has authored technical articles for national journals, and routinely speaks to electronic professional societies.

 
   

   
 

©1996 - 2011, 2012, 2013, 2014, 2015, 2016 by Zephyrtronics®. All rights reserved. The information, text, images, photographs, charts, graphs you receive online from Zephyrtronics® are protected by the copyright laws of the United States. The copyright laws prohibit any copying, redistributing, retransmitting, or repurposing of any copyright-protected material. Zephyrtronics is the registered trademark property of JTI, Inc. "The Science of Zephyrtronics" and "Simplicity Through Innovation" and "Zephlux" and "ZeroLead" and "Zero Balling" and "Zero Residue" and "Post Cooling" and "Post Cooler" and "AirBath" and "SolderGlide" and "SolderMill" and "Just So Superior" are the protected trademark property of JTI, Inc. "Zephyrtronics" and "Low Melt" and "Air Fountain" and "Fountainhead" are the registered trademark properties of JTI Inc. *The above names are the registered property of their respective owners.

 
 
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Updated for August 24, 2016