Collaborative Robots

Review of Collaborative Robots from Marcelo Chirai

ABC do Osciloscópio

ABC do Osciloscópio from Marcelo Chirai

Rugged computing terminology and standards

 

Rugged computing terminology and standards
(by Conrad H. Blickenstorfer)

What's an IP rating? Ingress Protection? How is that measured, and what does it mean? What does "intrinsically safe" mean? How do they do drop tests and such? Where can you find information on testing procedures? What are NEMA ratings? What does RoHS mean, and is it important? (Yes, especially if you deal with European markets). And what's FIPS 201? Or does a client request adherence to IEC 60601? Or what does a vendor need to do to comply with MIL-L-85762A for night vision imaging systems?

All of these terms, and more, you'll encounter in this specifications and sales pitches of rugged computing equipment. Knowledge of what it all means is crucial to understanding the potential suitability of equipment for your applications, and also when discussing your needs with a vendor.

In this section you'll find explanations of the many definitions and terms used in rugged computing, and also information on the various rating systems employed to indicate ruggedness, sealing and other environmental protection. You'll also find descriptions and updates on enabling technologies, such as outdoor-readable notebook computers screens.

You also find primers of a variety of ancillary technologies, such as RFID, bar code scanning, and others. What you see now is just the beginning. Over time we'll be adding additional definitions, primers, and white papers.

Vendors: If you have Technology White Papers which you'd like to share with potential clients, please email us at cb@pencomputing.com.

At RuggedPCReview.com we consider the Ingress Protection rating to be especially important. It is in the IEC (International Electro technical Commission) 60529 international standard and classifies how well electrical enclosures are protected against intrusion of solid objects, dust, and water. When used to indicate sealing of rugged computers, the IP rating tells you whether dust or water can get into your computer. Below is the IP rating table.

IP (Ingress Protection) Rating Table

	SOLIDS (1st number)		LIQUIDS (2nd number)
0	No protection	0	No protection
1	Protected against objects > 50mm (hands)	1	Protection against dripping water or condensation
2	Protected against objects > 12mm (fingers)	2	Protection against water spray 15 degree from vertical
3	Protected against objects > 2.5mm (tools/wires)	3	Protection against water spray 60 degree from vertical
4	Protected against objects > 1mm (small tools)	4	Protection against water spray from all directions
5	Protected against dust, limited ingress	5	Protection against low pressure jets of water
6	Totally protected against dust	6	Protected against heavy seas
7	N/A	7	Protection against the effects of immersion (6 inches to 3.3 feet)
8	N/A	8	Protected against continuous immersion (but under conditions defined by the manufacturer)

What is the MIL-STD-810F

It is an equipment testing standard by the United States Department of defense. It describes in detail testing procedures designed to determine how equipment holds up under a variety of conditions the equipment may encounter while being used, transported and stored. These conditions include temperature, impact, vibration, humidity, and more. Note that while the standard is extensively used for testing of rugged computing equipment, it was not specifically designed for that type of equipment. As a result, some tests are ambiguous when applied to computing equipment.

What is the difference between MIL-STD-810F and MIL-STD-810G?

MIL-STD-810F was introduced on January 1, 2000. MIL-STD-810G was introduced October 31, 2008, and supersedes MIL-STD-810F. The two documents are not substantially different, but different enough so that many testing procedures have different articles and numbers. As of late 2011, most rugged manufacturers have switched to providing ruggedness testing information using MIL-STD-810G, but some still cite the older standard.

What's MIL-STD-810F Method 506.4 (Rain)?

Manufacturers often refer to MIL-STD-810F Method 506.4. The MIL-STD-810F is a Department of Defense document that describes test methods for environmental engineering considerations and lab tests in great detail (Note that MIL-STD-810G, issued October, 2008, has superseded MIL-STD-810F). Method 506.4 describes testing to determine how well a piece of equipment is protected from rain, water spray, and dripping water.

Procedure I tests resistance to rain and blowing rain, with variations up to 45 degrees from the horizontal.

Procedure II sprays all exposed surfaces with water for not less than 40 minutes per face.

Procedure III drips water from no less than 3 feet for 15 minutes.

What's MIL-STD-810F Method 509.4 (Salt Fog)?

Salt fog can quickly ruin equipment. 509.4 describes testing methods to determine the effectiveness of protective coatings and finishes on materials for corrosion, electrical effect and physical effects. It can also determine the effects of salt deposits on the physical and electrical aspects of materiel. The product is exposed to salt fog mist from a 5% salt solution via atomizers at about 95 degrees Fahrenheit for a minimum of four alternating 24-hour periods, two wet and two dry. The product is then examined for salt deposits that can clog or bind components, electrical malfunction, and potential short and long-term impact of any observed corrosion.

What's Intrinsic Safety?

Intrinsic safety is a requirement that may be applicable to devices that are being operated in areas with flammable gases or fuels. It means that the device is incapable of igniting those gases. In short, an intrinsically safe piece of equipment won't ignite flammable gases, See our Intrinsic Safety page, and for more detail ecom instruments' intrinsic safety section.

What's MIL-STD-810F Method 510.4 (Sand and Dust)?

Specs also often include references to MIL-STD 510.4. Those are tests that evaluate the ability to resist the effects of dust that may obstruct openings, penetrate cracks, crevices, bearings, and joints and to evaluate the effectiveness of filters.

Procedure I tests if the device can keep out blowing dust.

Procedure II determines if it is sealed against blowing sand.

Procedure III tests what happens if dust settles on the computer as that can affect heat dissipation or clog up filters.

What's MIL-STD-810F Method 516.5 (Drop)?

MIL-STD-810F 516.5 also often appears in ruggedness specs. This tests a device's ability to survive a variety of impacts and shocks. MIL-STD-810F Method 516.5 defines the purpose of the shock test to "provide a degree of confidence that materiel can physically and functionally withstand the relatively infrequent, non-repetitive shocks encountered in handling, transportation, and service environments."

Procedure IV -- Transit Drop -- is especially popular with rugged computing equipment vendors and commonly called "drop test" or "drop spec." The test requires that items weighing 100 pounds or less survive a total of 26 drops on each face, edge and corner. The 26 drops can be divided among up to five samples of the same test item, which probably means used the first until it fails, then start with the second, and so on, although the language is not clear. Drop distance generally depends on "how materiel in the field might commonly be dropped." Table 516.5-VI (Transit Drop Test) shows that items weighing less than 100 pounds with a largest dimensions of less than 36 inches, i.e. virtually all mobile computers, must be dropped from 48 inches because "a light item might be carried by one man, chest high; thus it could drop 122 cm (48 inches). It also appears that the test is conducted with the equipment off.

While most manufacturers test using Procedure IV (Transit Drop), testing according to other procedures might make more sense:

• Procedure I (functional shock) test is designed to "test materiel (including mechanical, electrical, hydraulic, and electronic) in its functional mode and to assess the physical integrity, continuity and functionality of the materiel to shock." It also says that the intent of Procedure I is to disclose equipment malfunction that may result from shocks experienced by materiel during use in the field. Eben though materiel has successfully withstood even more severe shocks during shipping or transit shock tests, there are differences in support and attachment methods and in functional checking requirements that make this test necessary. A shock apparatus is used and equipment must remain functional with a sawtooth pulse of at least 40G for 11ms (truck/vehicle-mounted 20G).
• Procedure III (fragility) is designed "to determine the maximum level of input to which the materiel can be exposed and still continue to function...". In Procedure III, drop height is defined as "the height from which the materiel might be dropped in its shipping configuration and be expected to survive." "Suggested drop height" for items up to 20 pounds is 30 inches.

Realize that all these MIL-STD-810F 516.5 procedure were really designed to measure the effectiveness of packaging, so applying this to dropping actual devices is a bit of a reach. And simply stating that a device is "tested according to MIL-STD-810F" by itself means nothing. Detailed explanation as to what was tested and what the outcome was must be included, and as a minimum, Procedures I and IV should have been done and passed.

Note that according to the DOD, field data suggests that a typical piece of equipment will be dropped from heights up to four feet an average of four to six times during its life cycle.

What other MIL-STD-810F tests are there?

The MIL-STD-810F is a very comprehensive document. As a result, a statement saying a device is "MIL-STD-810F tested" doesn't provide enough information. The MIL-STD-810F is an almost 600 page document with tests for about two dozen things that can affect a piece of equipment. The tests are:

• 500.4 Low Pressure (Altitude)
• 501.4 High Temperature
• 502.4 Low Temperature
• 503.4 Temperature Shock
• 504 Contamination by Fluids
• 505.4 Solar Radiation (Sunshine)
• 506.4 Rain
• 507.4 Humidity
• 508.5 Fungus
• 509.4 Salt Fog
• 510.4 Sand and Dust
• 511.4 Explosive Atmosphere
• 512.4 Immersion
• 513.5 Acceleration
• 514.5 Vibration
• 515.5 Acoustic Noise
• 516.5 Shock
• 517 Pyroshock
• 518 Acidic Atmosphere
• 519.5 Gunfire Vibration
• 520.2 Temperature, Humidity, Vibration, and Altitude
• 521.2 Icing/Freezing Rain
• 522 Ballistic Shock
• 523.2 Vibro-Acoustic/Temperature

Each test has various procedures and methods, and each may or may not be relevant to a particular application. Major rugged equipment manufacturers have their own testing labs where they can conduct MIL-STD-810F testing. This is generally done in conjunction with testing in an independent lab.

What is the MIL-STD-3009?

MIL-STD-3009 (also referenced as DOD-STD-3009) is another standard manufacturers of rugged equipment may refer to. It sets requirements for aircraft display equipment for use with night vision imaging systems. For mobile computers that generally means they must not interfere with night vision equipment in a cockpit.

Part of this document is the U.S. Navy MIL-HDBK-87213 Revision A (Electronically/Optically Generated Airborne Displays) that describes, among other, criteria for legibility of electro-optical display equipment and daylight readability in bright environments, which is a military requirement. This can be an issue with daylight readable displays marketed to the government and armed forces.

What is ASTM 4169?

At times, rugged product descriptions refer to ASTM 4169, Truck Transport, 11.5.2 Random test, Assurance Level 2. ASTM stands for American Society for Testing and Materials and the 4169 standard sets tests and requirements for strength, durability and protective capability of packaging. Level II stands for medium test intensities (Level I is highest and Level II lowest) and is most commonly used.

What is the MIL-STD-461E?

MIL-STD-461E establishes interface and associated verification requirements for the control of the electromagnetic interference (emission and susceptibility) characteristics of electronic, electrical, and electromechanical equipment and subsystems designed or procured for use by activities and agencies of the Department of Defense. The standard primarily applies to electronic enclosures no larger than an equipment rack, electrical interconnections between enclosures, and electrical power input from prime power sources.

Rugged computer manufacturer AMREL created a useful white paper on MIL-STD-461E here.

What is UL 1604?

You may come across references to UL 1604. This is not a governmental or industry association standard, but a certification by Underwriters Laboratories Inc. UL is an independent product safety certification organization that has been testing products and writing standards for product safety for over a century. They have over 60 testing labs and have developed over 1000 standards. UL 1604 is a certification document and covers equipment, circuits, or components intended for use in hazardous locations. This basically deals with a unit's safeguarding against causing ignition of specified flammable gas- or vapor-air mixtures.

What does "embedded" mean?

There are various definitions. "Embedded" is often used for products or projects where the computer is just part of a larger system, and not a standalone PC. Intel uses the term differently. For them, "Embedded indicates that Intel anticipates shipping the product for an extended period of time. Embedded parts typically need to be procurable for 7+ years, whereas standard parts are typically procurable for 2+ years."

What is "PCI compliance"?

In the payment processing industry, PCI stands for "Payment Card Industry." The PCI has the "Payment Card Industry Data Security Standard" (PCI DSS), which is a set of requirements designed to ensure that all companies that process, store or transmit credit card information maintain a secure environment. PCI also issued the Payment Card Industry Security Standards Council (PCI SSC) to cover the ongoing evolution of the transaction process. See the PCI Compliance Guide here.

Why is altitude testing important?

Testing procedures designed to ascertain the ability of a piece of equipment to operate at high altitude are described in MIL-STD-810G Method 500.5 2.3.1 b(1). However, that test arbitrarily uses 15,000 feet, which is more than the 7,000 feet atmospheric pressure in a commercial airplane, but a good 2,000 feet less than even Mt. Everest's base camp. Why does it matter whether a piece of rugged computing equipment can operate in high altitude? Because at 19,000 feet, air pressure drops to half from what it is at sea level, meaning there are half the air molecules available for cooling and any other operation that requires air pressure for normal functioning.

What is the difference between OEM and ODM?

OEM stands for Original Equipment Manufacturer and describes a company that designs products according to their own specifications, builds them, but the products are then sold by another company under that company's name or brand.

ODM stands Original Design Manufacturer and describes a company that builds a product based on another company's design and specifications.

http://www.ruggedpcreview.com/2_definitions.html

BGA Solder Ball Shelf Life

 

August 24, 2015

I believe BGA Solder Balls are a homogeneous mass of metals, why is the shelf life only two years? With proper handling and storage, can the shelf life be extended?

V.P.

Experts Comments

 

The solder alloy itself should not change composition significantly over a period of several years. The main potential issue is oxidation of the surface of the BGA solder ball. Even when stored properly air will eventually make its way to the solder surface and oxidation will occur. As the oxide layer grows the balls will become more difficult to solder. The rate of oxidation is slow enough that the balls will be usable for at least two years, but may be difficult to use after that time.

Tony Lentz Field Applications FCT Assembly Mr. Lentz has worked for FCT Companies for 14 years as a Lab Manager and Facility Manager. Over the last 2 years he has worked in Field Application for FCT Assembly. He holds BS and MBS degrees in Chemistry.

The shelf life, as defined by the manufacturer, takes into account all aspects of the package, but let's stick to the solder ball characteristics. You are correct that the balls are a homogeneous alloy. So what might degrade after two years? Assuming that the parts are stored in MBBs compliant to J-STD-033, moisture will not play a role; the MBB and desiccant will protect against moisture ingress for approximately three years. The MBB does not, however, protect against oxygen, and the surface of the balls will oxidize over time. It is very likely that, after two years properly stored, solderability will be quite acceptable. It's just not guaranteed. Can we extend this time? The answer is, certainly we can, if we exclude oxygen. For long-term storage of parts for aerospace applications, where a program needs to be supported for a decade or more, we use nitrogen inerted cabinets, which both exclude oxygen and moisture. This eliminates surface degradation of parts. It does not, however, eliminate growth of intermetallic compounds, which will occur over time. IMC growth only impacts solderability when it grows through to the surface, however, which is something you won't see on BGAs. Bear in mind that any steps you take to extend solderability still don't affect the warranted period for solderability, only the practical life.

Fritz Byle Process Engineer Astronautics Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.

Unfortunately solder suppliers have no control how their products are handled once they leave the factory. Also, the products are shipped to a wide variety of locations and climates including humid areas as well as locations near salt water. With this knowledge, the solder has to protect against returns involving old and oxidized product. For this reason these forms of solder are assigned a shelf life. With that said, the assigned shelf life is often conservative, and the product, if stored and handled properly and used with a flux, are usable well beyond the stated shelf life. I often encourage the end user to establish an internal protocol to recertify or lengthen the shelf life of the product. This would typically involve simple wetting tests with fluxes and substrates representative of what is used in their actual products. Some solder suppliers offer testing to "recertify" the product. However, the fee for so doing, is often near or close to the cost of just buying new product.

Eric Bastow Senior Technical Support Engineer Indium Corporation Eric is an SMTA-certified process engineer (CSMTPE) and has earned his Six Sigma Green Belt from the Thayer School of Engineering at Dartmouth College. He is also a certified IPC-A-600 and 610D Specialist. He has an associate's degree in Engineering Science from the State University of New York and has authored several technical papers and articles.

Many BGA manufacturers have a standard 2-year shelf life for their products.  I have also seen others which recommend just one year. Proper handling and storage may extend the life of the BGA but it is not a predictor of its performance and reliability.  One way of predicting shelf life would be to expose the components to some type of accelerated aging process to see if there is a change in component's physical properties along with its performance within the circuit.

Edithel Marietti Senior Manufacturing Engineer iDirect Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.

http://www.circuitnet.com/experts/87700.html

The War on (SMT) Failure

The war on failure from Marcelo Chirai

Accelerometer Mounting Accessories

Many accelerometer adhesives have been successfully used for securing mounting bases to test objects. These include epoxies, waxes, glues, gels, and dental cement. Some provide more permanent attachment than others. Stiffer adhesives provide better transmission of high frequencies. Adhesives should be selected which perform adequately for the required application and environmental conditions. PCB® offers petro wax and quick bonding gel. How do I remove an accelerometer adhesive mount sensor? Obviously, the mounting of an accelerometer is critical to a successful measurement. Accelerometers have a cost.  You want to protect your investment.  The proper removal of an accelerometer extends its useful life. Improperly removing the sensor may cause immediate damage and failure. Do not use an impact technique (hammer, chisel, knife) to remove the sensor. Soften the adhesive first by use of a debonding agent. Then use a removal tool by gently twisting the accelerometer free of its mount.  To avoid damaging the accelerometer, a debonding agent must be applied to the adhesive prior to sensor removal. With so many adhesives in use (glues, dental cement, epoxies, etc.), there is no universal debonder available. The debonder for the Loctite 454 adhesive that PCB® offers is Acetone. If you are using anything other than Loctite 454, you will have to check with the individual manufacturer for the debonding recommendation. The debonding agent must be allowed to penetrate the surface in order to properly react with the adhesive, so it is advisable to wait a few minutes after applying before removing the sensor.

http://www.pcb.com/TestMeasurement/Accelerometers/Access/Adhesives.aspx

Calculation of a Shock Response Spectra

Calculation of a Shock Response Spectra from Marcelo Chirai

Excess Flux Residue After Hand Soldering

July 10, 2015

We observe an excessive amount of flux after hand soldering terminals using flux cored wire solder. See the image.

Is this amount of excess flux normal?

Is there something wrong with our manual soldering operation?

K.K.

Experts Comments

The answer is it depends but this appears to be excessive on the contact, but was a different amount of solder wire or larger core used to solder the sample. I would be more concerned is the flux benign or still corrosive (no clean flux requires additional heat to complex the flux to create a benign residue and this looks like it is far from the solder joint heating). The other question to ask if this is insulative do you want it on the contact that is designed to make electrical contact.

Terry Munson President/Senior Technical Consultant Foresite Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.

The picture shows flux residue from soldering using solder wire which is not uncommon. Flux residue will depend on the percentage of flux in the wire. Flux percent by weight will vary from 0.5% to 3% in solder wires and higher percentages will leave more visible flux residue. Less flux in the wire, less flux residues, however you need a good percentage to enable ease of soldering. Usually 1, 2 or 3 % flux is best with 0.5% being more difficult to use by operators. If the residue is from flux that are no-clean in nature the residue will not cause issues normally. Most no-clean solder wires are described as ROL0. No-clean, RA, RMA flux wires have fluxes which are resin based and slightly higher or lower soldering tip temperatures will not impact the volume of visible flux. Resins tend to have high boiling points and do not vaporize with soldering tip temperatures. If temps are too high the resin will darken and burn. This will render it harder to clean off later.

Peter Biocca Senior Market Development Engineer Kester Mr. Biocca is a chemist with 24 years experience in soldering technologies. He has presented around the world in matters relating to process optimization and assembly. He has been working with lead-free for over 8 years. He is the author of many technical papers delivered globally.

Flux residue is proportional to the percentage of flux in the wire and the amount of wire fed into the joint. Wire solder that is '2% flux core' is 2% flux core by weight - it's approximately 50% by volume. Therefore, if the joint accepts a lot of solder, then there is going to be more residue. In the image you provided, the terminal looks to hold a lot of solder therefore you could expect more visible residue, but I would not consider it excessive. You could experiment with different manufacturers wire solder products to see if they leave less residue as flux formulation can significantly impact location/appearance/volume of residue.

Tim O'Neill Technical Marketing Manager AIM Tim O'Neill is the Technical Marketing Manager for AIM Products. AIM is a global supplier of materials for the PCB assembly industry including solders, fluxes and thermal management materials. Tim has a B.A. from Assumption College and post-graduate studies in education. He has 20 years of experience in the electronics soldering industry, beginning his career in 1994 with EFD and was key in business development of their fine pitch solder paste dispensing technology. Tim joined AIM in 1997 and has since assisted many clients with assembly challenges, specializing in Pb-Free process development and material selection.

First, it is assumed that this is a No-Clean flux-cored solder wire.  If not, then the residue would have to be removed. If this is a No-Clean flux-cored solder wire there is nothing wrong with your soldering but ways to make it look better. Seeing that the flux-cored solder wire has been heated fully to alloy melting, the flux within has been heated sufficiently to Remove oxides as is needed for joining and Remaining flux residue will be fully activated and rendered harmless in terms of corrosion.  The amount of residue can be controlled somewhat by adjusting the diameter of the flux-cored solder wire. Try using a smaller diameter for less flux residue; the smallest diameter that will do the job. The IPC-610 standard for workmanship allows flux residue resulting from hand-or machine-soldering as long as the residue has been heated sufficiently to activate it. Any surface that has achieved soldering temperature will certainly render the flux residue activated.

Gary Freedman President Colab Engineering A thirty year veteran of electronics assembly with major OEMs including Digital Equipment Corp., Compaq and Hewlett-Packard. President of Colab Engineering, LLC; a consulting agency specializing in electronics manufacturing, root-cause analysis and manufacturing improvement. Holder of six U.S. process patents. Authored several sections and chapters on circuit assembly for industry handbooks. Wrote a treatise on laser soldering for Laser Institute of America's LIA Handbook of Laser Materials Processing. Diverse background includes significant stints and contributions in electrochemistry, photovoltaics, silicon crystal growth and laser processing prior to entering the world of PCAs. Member of SMTA. Member of the Technical Journal Committee of the Surface Mount Technology Association.

The amount of flux does not seem excessive. Soldering this type of terminal requires a fairly high volume of solder, so there will be more residue than for a smaller joint. It may be possible to reduce the amount of residue by purchasing solder wire with a lower flux percentage. Speak with your solder manufacturer about what you are now purchasing, and whether a version with lower flux percentage is offered. If it is, you will need to test it to see whether the reduced flux activity due to less flux is adequate for the application. One other thought; if the flux running down the terminal is of concern, re-orienting the terminal during soldering may avoid this, but of course the residue will still be present.

Fritz Byle Process Engineer Astronautics Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.

From the photo is appears that your operator is adding flux prior to hand soldering. The flux is too far away from the solder joint so I would check this first. If this is not the case, from the photo it appears that the flux is not activated (as shown) which could mean: Soldering iron temperature is too low. Soldering time on the joint is too short and not activating the flux. Flux content in the solder core is too great. Perhaps considering a lesser percentage.

Gary Goldberg President and CEO PROMATION, Inc. Mr Goldberg has practical experience in production line layout, process flow and cycle rate analysis. He knows how to avoid bottle necks and most related PCB or pallet handling questions.

To determine if the electrical performance will be compromised, a surface insulation resistance test (available in the IPC Test Methods) will show if the residue will be sufficient enough to compromise the finished PCB. Hand soldering temperatures can vary significantly.  Soldering tip in relation to board density (which can act as a heat sink) , not to mention the human factor, can add up to inconsistent heating ultimately leading to excessive residue.

Stephanie Nash Director Integrated Ideas & Technologies, Inc. Stephanie Nash is the Director of Technical Services & Marketing for Integrated Ideas & Technologies, Inc., a premier manufacturer of SMT stencils. She has been instrumental in the stencil design and technical support.

http://www.circuitnet.com/experts/87080.html

Sensor Overloading Tip

Sensor overloading tech tip from Marcelo Chirai

Solder Joint Opens - What To Do?

 

Electronic components are soldered to circuit boards every day and in some cases opens are found during x-ray inspection or during the test. You may be inclined to re-heat and reflow the solder using a little extra flux. It's reasonable to think this will work but it can be deflating when it is not effective.

In a desperate attempt to correct the defect, the process may be repeated at higher temperatures or for a longer cycle. Yet again, the opens may remain.

While attempts at secondary reflow may often work successfully, it will not work when there are pads with high levels of oxidation. The only way to reliably rework this type of defective solder joint is to remove the component, condition the pads by removing the oxidation followed by tinning, and finally reinstalling the component.

Partially wetted pads.

Multiple heat cycles not only overheat the components, but also overheat the pads and soldermask, especially when higher lead-free solder temperatures are required. Adjacent components and solder joints can also be impacted negatively.

Damage to component packaging, fractured solder joints, and base board discoloration are some common side effects. It is a perplexing situation. Ask anyone who has pressed down on a component with an open to see it function properly but then when the pressure is removed, the open returns.

The best practice after the first attempt at secondary reflow is to either remove the component and investigate the situation or send the circuit board to a specialist for rework.

Several members of the Circuit Technology Center team contributed to this feature story.

http://www.circuitrework.com/features/825.shtml