We search for industry news, so you don't need to. HOME EXPERTS NEWS PAPERS PRESS SEARCH SUBSCRIBE ARCHIVE/TRANSLATE Ask the Experts Panel   Questions Index  ■  Submit a Question  ■  Experts Panel  ■  Join the Panel 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. Fritz Byle has submitted responses to the following questions. Application Using No-Clean and Water Soluble Fluxes You'd need to be absolutely sure that you removed all of the water soluble flux residue, as any remaining residue ... What's Causing Cloudy Conformal Coating It's clear (pun intended) that the conformal coating has been degraded in the area between the leads, and that an ... Allowable Bow and Twist on Round PC Fab My approach would be as follows: Calculate the dimensions of the largest square you can draw on the circular part ... Reflow Oven - 5 Zone or 8 Zone From a practical perspective, five (heating) zones is certainly enough, given that the length of the zones is configured properly. ... Moisture Sensitive Components in Flooded Storage Facility Short answer, there are probably alternatives. Whether they are worth it depends on the value of the components, including their ... Insufficient Barrel Fill on Through-hole Components I'll assume that this is a wave soldering process, and not a selective soldering process (though the concerns are similar). ... SMT Target Component Placement The key question is whether the location of the LED is shifted prior to reflow, or shifting during reflow. You ... How to Re-qualify BGA Spheres The pertinent question to consider is, what physical processes do we expect might degrade performance of the spheres, and have ... Cleaning Under Low Clearance Components Yes, your fears are absolutely justified. Residual water-wash flux is very corrosive, and it will be near impossible to ensure ... What Caused SMT Pads to Oxidize After Reflow There are three possibilities here:  The finish was ENIG, but the gold was improperly applied (too thin) or the gold ... Moisture Sensitivity Level for Bare Boards You are correct that the MSL of the bare board can vary; the factors affecting moisture sensitivity, roughly in order ... Specific Solder To Control Dendritic Growth It's certainly not unheard-of for a customer to specify which solder paste to use. Contract manufacturers tend to not like ... Solder Balling Splash After Reflow The small, uniform size of most of the balls visible on the x-ray image strongly suggests to me that they ... IPC-A-610 Class 3 - IPC-A-600 Class 2 Yes, they are different requirements. If we can make the case that a PWB designed and inspected to IPC-A-600 Class ... What Is This Contamination? There is almost definitely corrosion going on, so the question is what is the source? From what we can see, ... Frequency of Temperature and Relative Humidity Tracking There's no standard that I'm aware of. From a practical standpoint, it's very dependent on the physical characteristics of your ... BGA Placement Paste or Only Flux The flux-only scenario has been used for many years for flip-chip and for fine-pitch BGA mounting to some degree. It ... Solder Paste Thickness Measurements It's a conundrum, to be sure. In an ideal world, we want to be certain that the volume of paste ... Reliability Concerns When Converting to Lead-free In my opinion, yes, there is reason for concern. There has been some research that suggests that Pb content in ... Old Components and Blow Holes I can certainly see old components causing wetting problems. If the wetting problems are spotty, localized issues and some happen ... What Is Causing Connectors to Bow? I'm carefully scrutinizing the image, and based on what I can see, it looks like the last 5 or 6 ... How To Reduce Solder Joint Voids in QFN Components Window-paning is the accepted method of optimizing the solder paste deposition for the large pad under QFN components. The optimal ... Is Solder Mask Considered an Insulator Solder mask should never be considered an insulator. It can have porosity and pinholes, and we should therefore not consider ... Solder Mask Thickness Tolerance The 0.8-mil thickness is probably near the higher end, but in range for a photoimageable mask, provided that the measurement ... Question About PPM Defect Rate for Reversed Packages We'll have to assume that we are ruling out "systematic" errors, e.g. an entire reel of parts loaded opposite of ... Using Solder Paste Beyond the Expiration Date A white powder suggests to me a metal salt. If the powder is on the board (outside the solder joint) ... Concerns With Silver Finish Component Leads Silver as an alloying addition to SnPb solder will change the mechanical properties of the solder, making it somewhat stronger ... Selective Solder System Purchased At Auction Really the best solution is to replace the pot. A pot designed for SnPb solder may not be appropriate for ... Problems With Large Voids There are several possible contributing causes for the large voids, including: Lack of egress for gasses generated during reflow Higher ... Ultrasonic Cleaning and Surfactants In short, yes. Deionized water does have a high surface tension, and because the ultrasonic cleaning process relies on cavitation, ... Partially Visible or Hidden Solder Connections In situations similar to the one you show, it is often possible to get a very good estimate of the ... Initial Screen Print Test Board There are a couple reasons why it might be a good idea: It will get the paste roll worked (sheared) ... Components Falling Off During Wave Soldering I'm not at all familiar with lacquer coating, but that should be of little importance. Here's what to look for: ... Mixed Process Solder Joint Appearance, Smooth or Grainy? The appearance of the final joint depends on the make-up of the non-SnPb finish on the part, and the amount ... Environment Impact on Assembly, Printing and Reflow The majority of SMT assembly areas are not formally controlled to a particulate count. That said, the particulate levels in ... Soldering Components with Silver Pads Since you state that the silver dissolves into the solder, I will assume that there is more than an immersion ... 0201 Pick & Place Nozzle Plugging First, you are correct that you should carefully consider the transition to a 0.004" stencil. There will be an impact ... BGA Solder Ball Shelf Life The shelf life, as defined by the manufacturer, takes into account all aspects of the package, but let's stick to ... Tough Hand Soldering Problem The "land" area for the wire attachment is typically made of the same material as the grid. Depending on the ... Selective Soldering Frame Causing Cold Solder Joints Yes, absolutely. Most wave soldering systems are a little challenged with getting adequate preheat and maintaining it across the gap ... Conformal Coating in Nitrogen Environment Without very specific knowledge of your process, including the coating materials involved, my comments must be rather general. The main ... Viscosity of Solder Paste Before Printing Short answer... the one that works (four that paste). Long answer we could write a textbook on. In essence, the ... QFN Test Failures Caused by Flux Short answer, we can't rule it out. At high frequencies, typically above 1 GHz, some flux residues can create losses ... Can a Few Contaminated Joints Cause an Assembly to Fail RoHS Compliance? If you regard all of the solder as one separable component of the assembly, I guess you could conclude that ... Bottom Terminated Components and Vias First and foremost, tenting on both sides without filling is not recommended. There is a high risk of entrapped chemistry ... Wave Soldering System Nitrogen Use You'll need some type of flow meter somewhere. The best solution is an electronic, totalizing flowmeter installed directly upstream of ... Copper Dissolution Rate You're right... everyone seems to have a different number for the rate. This is because the test methods used vary ... PCBA Inspection Process Causing Damage I'd agree that any time we slide a PCBA across a surface, there is some risk. If the surface is ... What is the IPC Definition for Uncommonly Harsh? The language here may seem very vague, and there is, I think, actually a good reason for this. I don't ... Floor Life of MSD Parts Since you specify 168 hours as the floor life, I will assume that your devices are MSL 3. You probably ... Gold Edge Contact Rework The "residue" might actually be a surface condition caused by the plating conditions, usually by plating too quickly (too high ... Gold Plating and Embrittlement Whether there is a risk of embrittlement depends on several variables: Amount of gold expected to be leached (soldered area*gold ... Overlap Solder Joint Failures The description of "cold" solder joints is not conclusive as to root cause, however that should not prevent us from ... Solder Paste Prep Before Use In order to determine if your warm-up time after removal from refrigeration is adequate, insert a temperature probe into the ... Tiny Solder Balls After Reflow The most likely culprit here is the volatile materials in the solder paste. It's not the only possibility, but you ... Hand Soldering at Low Temperature First, let's look at the impact on the "delta-T," or the temperature difference between the board and the soldering tip. ... Solution for Grape Effect There are two possible causes for the rough surface of solder joints on the smaller components: The flux is being ... Component Damage From IR Reflow I suspect that this is the same issue that I have seen on another component type in the past. The ... Exposed Copper Risk In a word, yes, you should be concerned. The level of risk really depends on the enclosure and operating environment. ... Manual or Automated Assembly? Even moderate levels of automation can have huge benefits. I would definitely recommend starting to move down the path to ... Pin in Paste Solder Dropping Your main contributing causes to this problem are likely to be as follows, in approximate order of importance: Pin geometry ... Removal of Coatings from PCBs The short answer to this question is "use the materials and process recommended by the coating manufacturer." It truly is ... V - Scoring PCB Question I've not heard of anyone doing the scoring after SMT, though I’m sure it has been done. I can’t think ... How To Rework SMT Connector with Center Ground Strip Normally we remove these using a hot-air rework station. If the board is high-mass (very thick), pre-heating the board to ... Cause of Incomplete Solder Reflow It's very hard to tell from the tiny photo, but it looks like the roughness is confined to the solder ... Solder Paste Past Shelf Life If you do not have internal capability to re-certify the material, contact the manufacturer. They should be able to re-certify ... Concave Via Fillets Causing Problems In order to reduce or eliminate the dimples, we first need to list the root cause(es): Solder shrinkage during solidification ... Options for Reballing BGA Components I would re-ball using spheres and tacky flux. I would not use paste. There are two main reasons for this: ... MSD Components Baked Too Long The biggest risk of baking too long is loss of solderability. Many parts today have pure (or nearly pure) tin ... Conformal Coating Press Fit Connectors After review of the pertinent section of IPC-A-610, I actually don't see that there is any requirement for all soldered ... Production Floor Temperature and Humidity Loggers Whether one logger is enough is entirely dependent on the facility. In facilities where airflow into/out of the facility is ... Silver Solder for Audio Circuits I agree with Jerry K's points (2) and (3). In addition, let me offer some insight into what may be ... ESD Grounding - 1 Meg Ohm Resistor The 1-megohm resistance is used for two reasons: It limits the speed that charge is passed, avoiding rapid discharge of ... What Is Acceptable Bending For Assembled PCBs? The limits of acceptable bending depend strongly on the type and size of components mounted. BGAs in particular are sensitive ... Rechecking Thermal Profiles Yes, you should periodically run a thermal profile. With the controls in place on most modern convection-based ovens, the risk ... Mixing Silicone and Acrylic Conformal Coatings In a word, "yes." Adhesion of the acrylic to the silicone material, or to any residues left after removal of ... Soldering Station Calibration Personally, despite what the manufacturer says, I would still verify that they are within tolerance at the desired setpoint, and ... Minimum Component Lead to Lead Spacing for Wave Soldering The minimum practical pitch for multi-lead components such as connectors is about 1.27mm (0.050”); I have not personally dealt with ... Frequency of Checking Solder Paste Viscosity There are some issues that make checking viscosity less useful than it might be: Differences in the equipment used (manufacturers ... Wave Solder Pot Alloy Adjustment Formula I'll assume that you have room in the pot to make a small addition without first removing some. We will ... IPC 610 Class 3 with Missing Non-functional BGA Pads From an inspection standpoint, no, I don’t believe that boards with the non-functional lands meet the intent of the specification, ... Very Low Temp PCBs In general, you want to look at indium-based solder alloys. Pure indium is used for seals in cryogenic applications and ... Reduce Glare During Assembly Diffuse lighting is going to make the biggest difference overall. You may be able to reduce some glare by using ... Conformal Coating Recommendation Conformal coating is certainly one component to an environmental protection strategy. Some cautions here: Remember that conformal coating will not ... Excess Flux Residue After Hand Soldering The amount of flux does not seem excessive. Soldering this type of terminal requires a fairly high volume of solder, ... Circuit Board Bow and Twist There are four main possible causes to look at: Design (copper imbalance) Fabrication (process error) Support issues (sagging due to ... Rise of Bismuth Levels in our Solder Pots Could bismuth be coming from the components? Short answer, yes, it could. Is it likely? Not so much. I know ... ESD Conductive Floor Tile Worry If the worst case is defined as 10^4 (10k) ohms from source to ground, then there is most definitely a ... Lead-Free Solder Contaminated with Lead First, I completely agree that you need to address the root causes of the Pb contamination to avoid a recurrence. ... Suggested Limit for PCBA Heat Cycles The answer is "it depends." We can think about rework cycles as taking up some portion of the useful thermo-mechanical ... Solder Mask Ghosting Like you, I am skeptical that you've got the same problem across multiple suppliers and PWB types. Seems much more ... Test Probe Problems After Pin-In-Paste You are correct suspecting that you are addressing the symptom and not the root cause, but addressing the root cause ... Burned Chip Repair In general, whether you can effectively make the repair depends on: Gaining access to the replacement part, Determining that the ... Confused About IPC-A-610 Class 2 vs. Class 3 I agree that the classes in the IPC-A-610 (or the J-STD-001 document for that matter) are completely unrelated to whether ... Bottom Side Chip Bonding This is a really good question. In fact, there is a bunch of incorrect information out there on this. There ... Challenging Cleaning Problem Given that you really would prefer to clean due to your high-impedance circuitry, you need to find an economical, reliable ... Reflow oven testing and calibrating concern I agree with the responders that there is no real industry standard, and I also agree with the general sentiment ... HASL Surface Finish and Coplanarity For BGA components down to about 0.8mm pitch, HASL is an acceptable finish. Your component, with a 0.6mm ball diameter, ... Concerns Replacing High Speed Components with No-Clean Solder I'll assume that by 1GB you meant 1 GHz. In short, yes, there can be problems with some pastes. To ... Head-In-Pillow Reject Rate What's acceptable has a lot to do with the tolerance for failures in the specific product and application. Also, you ... Solder Caking to Bottom of PCBs After Wave Hard to say exactly, but if the problem appeared immediately after changing out the pot, I would bet on differences ... Octagonal Pads for 0402 Chip Caps I have not seen this exact strategy, but it does make sense. The octagonal pattern (effectively a square with the ... Selective Printing for BGA Components If the BGA is depopulated but PWB lands are present, sure, you can simply not print the lands where no ... What Causes Component Rotation During Reflow? The reason behind the rotation is unbalanced wetting forces. As the paste begins to reflow, it wets one side of ... Extending Shelf Life for Jars of Solder Paste The first course of action should be to talk with a technical resource at the manufacturer. It's highly likely that ... How to Eliminate Via Pits You have two things working against you here. The first and most important is that almost all alloys shrink during ... Bow and Twist Requirements The short answer is, whatever your contract with the customer says. If I assume that it says nothing about bow ... Legend Marking Discoloration The darkening is of course caused by thermal decomposition of the ink. This type of degradation is typically accelerated above ... BGA Joint Voids - Accept or Reject Let's first address the question of IPC-610 acceptability. The acceptability criterion for voiding in IPC-610 is currently <25% void area ... Pre-bake in a Vacuum Yes, in theory this will work. The vacuum will lower the boiling point of water vapor, and also decrease the ... Via Wall Thickness Test Yes, there is. The method commonly in use by PWB fabricators is the micro-resistance method. In commercially available equipment (e.g. ... Double Sided BG I'll assume that the BGAs are not back-to-back; if they are, that's another question entirely. If they are not back-to-back, ... Step Stencil Question You may find that you need a small increase in pressure. Whether you do or not depends on the design ... Dam & Fill vs. Conformal Coating A dam & fill strategy may be driven by a need for stronger environmental protection, for high voltage isolation, for ... Through Hole Connector Solder Joint Hole Fill Our company faces this problem daily since our products (aerospace electronics) use thick PWBs and PTH connectors with high pin ... PoP Assembly Options Of the two options presented, Option 1 results in one less reflow cycle for the entire assembly, and that is ... Removal of Non-functional Pads from Inner Layers An interesting question to be sure. Fabricators normally do prefer it, because it makes drilling easier. Copper is a tough, ... ESD and Humidification Let's do a thought exercise. Assume we have a workstation located in a very dry area, but otherwise configured with ... Solder Paste Viscosity If you decrease the particle size of the powder while keeping the metal percentage the same, the viscosity will increase. ... Spotting After DI Water Cleaning The spotting could conceivably be due to fine, insoluble material suspended in the water. Such material would not necessarily contribute ... Double Sided Reflow for Micro BGA Components Both convection and vapor phase are potentially good processes. In either case, PWB warpage during reflow needs to be controlled. ... Long Term Component Storage As an Aerospace & Defense OEM, we have the same requirements, and have implemented LTS (Long-Term Storage) protocols to deal ... Standards for Pin-in-Paste The answer to the pin-to-hole ratio question is usually to make the hole as small as tolerances will allow. We ... Reliability of Automated Soldering vs. Hand Soldering There are three main sources of differences in reliability: solder joint behavior, component damage, and cleanliness. Hand soldering can involve ... Cause of Green/Blue Oxide Buildup What you are seeing are most likely not oxides, but "metal salts" which are corrosion products. In a marine environment, ... What Are Realistic Guidelines for PCB Flexing? IPC A-600 applies only to unassembled PWBs. The reason for the reference to SMT boards is that raw PWBs that ... Stencil Cleaning Procedure The practical answer is "it is if they can show that it does the job." What you really care about ... Pin-in-Paste Problems It's difficult to give specific recommendations, since we don't know the exact geometry and materials of construction of the pin. ... Lifted Lead on SOT Component Assessing root cause on this defect is tricky. One or more of several possible causes may be in play. Let's ... Reflow Oven Calibration Schedule A good basic recommendation is to run a weekly profile, and to do control charting on the temperatures and timings ... A Generic Reflow Profile In general, no there is not. Through careful testing, you may find that you can narrow the number of required ... Reduced pH and Specific Gravity of Flux Let's take specific gravity first... if it is low, that means that there is more solvent and less solids present ... Epoxy Wicking up Wire Insulation Three opportunities present themselves: Modify or change the epoxy such that it does not wick Modify the curing process for ... Solder Paste Life on the Stencil You probably don't need to change it. I'll make the assumption that your 250g additions represent about half the volume ... White Legend Ink Turning Pink Let's think about the possible ways that a pink color could be generated: The ink picked up traces of a ... Toe Fillet Requirements on Gull Wing Components Per J-STD-001, there is no requirement: There is no reference to a minimum toe fillet height (Class 1, 2, and ... Dross Particles Sticking to PCBs If the pot surface has been cleaned, then the dross particles are coming from immersed parts. Dross often gets entrained ... Solder Paste Alloy Check The two biggest problems here are: Even a pretty "warm" SnPb profile is just barely above the melting point of ... Un-cleaned PCB Assemblies Potted There are two very different possible scenarios here: The flux used was a water-soluble flux The flux used was a ... Solder Balls During Rework I would need to see samples to be sure, but I would bet that the solder balls are forming because ... Transfer Efficiency Greater Than 100% Yes, it is possible for transfer efficiency actually be greater than 100%, and yes, it is possible that systematic error ... Cleanliness After Coating Removal Cleanliness here is a big concern, since urethane coatings normally require highly alkaline strippers to remove. The residues from these ... Pin-in-Paste Standards Normally you are struggling to get adequate paste volume and required volume increases as the square of the PTH diameter, ... Solder Popping Out of Holes It's hard to say for sure, not knowing more specifics of the PWB construction and the thermal history of the ... Zip-lock Bags vs. Heat Sealed Bags In a word, no. When the components are placed in the Moisture Barrier Bag (MBB) we'll assume they are dry. ... How to Remove Adhesive Bonded Resistors A "hot tweezer" adapter for a soldering station probably will do the trick for removal. It will heat both joints ... Voids with Back to Back BGA Components It's not uncommon for voids that may have been present at a size too small to detect to grow during ... Conformal Coating Over Heat Sinks Yes, definitely mask them; the coating will impede performance. The bulk thermal conductivity of a copper heatsink is close to ... Insufficient Barrel Fill on Through-hole Components If you search for generic recommendations on how much over-size your hole needs to be, you'll find a wide range ... Cause of Cracking on SOT23 Components It seems that mechanical damage after placement is the most likely scenario. Is the problem position near a board edge ... SMT Component Glue Strength There are two basic alternatives: Use a shear tester and shear the component off using a flat-faced rod to push ... Test for Flux Penetration What we used to do was to use a plate with perforations of various sizes arranged in a pattern that ... Improve DPPM for Wave Soldering Using Nitrogen It's possible that a nitrogen environment will improve performance. It's also possible that for some defect types it will increase ... BGAs Mixing Tin-Lead and Lead-Free In either case, if full mixing of the alloys is ensured by the reflow profile, reliability of the resultant joints ... Rework for OSP Assemblies I can think of one scenario where procedures might need to be modified; when rework needs to be performed on ... Deionized Water Sample Testing Absorption of ionic species such as CO2 from the atmosphere as well as very small amounts of contaminants from containers ... BGA Die and Pry Testing In short, I think it's unlikely that the root cause of the observed defect is Kirkendall voiding. What's needed for ... Options to Cut Inspection Time Without much more knowledge of your situation, my gut reaction would be to say "no." It's almost always better to ... Class 3 Cleaning Requirements The answer is "it depends." Whether or not you need to make any changes to cleaning operations depends entirely on ... Reflow of Double Sided Micro BGAs Before we discuss in detail what you need to do, let's first list the risks you have to deal with: ... Mixing Different SAC305 Solders If both of the manufacturers certify that their products conform to the requirements of J-STD-006, then the solders should be ... Solder Mask Mis-registration Issue Let's start with the industry specifications; IPC-6012 states that no encroachment of mask on non-soldermask-defined BGA lands is allowable, except ... Tacky Substance Under Zero Clearance Parts It is very normal for flux residue to remain under these low-clearance components and to potentially bridge between contacts, in ... Can Solder Joint Geometry Change Resistance? First and foremost, adding a resistance in the circuit should not increase the current. If you model it, you should ... Syringe Dispensed Solder Paste for Hand Soldering Syringe-dispensed solder paste can be an acceptable substitute for wire + liquid flux; some pastes work better than others for ... Fastening Surface Mounted Connectors Before or After Refow? As far as I know, there is no general guidance, due to the fact that each connector design is unique. ... White Discoloration After Ultrasonic Cleaning Your residue could be one of two things: Un-dissolved flux that has been attacked by the chemistry. Partially dissolved flux ... Blind Hole Pin Soldering It's definitely possible that gas will be trapped and out-gas as it expands. Depending on the exact geometry of the ... Reflow Causing Warp If you are stuck with the design, then the only recourse is to mitigate the warping. If there are mounting ... Black Land Edges I'll make the assumption that the Ni-Au finish is ENIG, meaning a very thin Au layer, less than 6µin. I ... Variation in Solder Paste Thickness I believe your answer lies in the "edge effects." The smaller aperture has an area ratio, AR(1) of 0.62. This ... Gold Plated Hole Defects It's almost always harder to fill open holes than holes with leads in them. The presence of a lead in ... Glued SMT Components Falling Off First, some key assumptions: There was in fact sufficient adhesive present. You've done a thermal profile of the curing process ... Soldering Multilayer Ceramic Chip Capacitors The degree of sensitivity of the ceramic cap depends on several things, including the body size and the type of ... Idle Wave Solder Temperature There are two significant downsides to cooling the pot below the solidification temperature: Repeated solidification and re-melting puts mechanical stresses ... Insufficient Plated Hole Fill with Electrolytic Capacitors Contributing root causes of this defect can be one or more of the following: Too many ties to inner ground ... HASL vs. Immersion Gold There is really no one-size-fits-all answer to this question. The answer for your application really depends on the following factors ... About Us | Advertising | Archives | Ask the Experts | Calendar | Contact Us | Custom Email Broadcast | Disclaimer | Exclusives | News | Press Releases | Press Release Submit | Privacy Policy | Search | Subscription | Technical Papers | Technical Paper Submit | Viewpoint Circuitnet Media, LLC 6 Liberty Square #2040, Boston MA 02109 USA Jeff Ferry, Publisher | Ken Cavallaro, Editor/Business Manager Copyright © Circuitnet Media LLC. All rights reserved. A Circuitnet Media Publication