DVD-71C IPC-A-610E Common Inspection Errors - IPC Training ...

DVD-71C TranscriptDVD-71CIPC-A-610E Common Inspection ErrorsBelow is a copy of the narration for DVD-71C. The contents forthis script were developed by a review group of industry experts andwere based on the best available knowledge at the time ofdevelopment. The narration may be helpful for translation andtechnical reference.Copyright IPC – Association Connecting Electronics Industries. All Rights Reserved.IntroductionFLOYD (on camera)Hi – I'm Floyd Bertagnolli. I’m an IPC-A-610 Master Trainer…. and President of STM, anauthorized IPC Training Center. After years of working with companies in ElectronicsAssembly…there appear to be certain common “misinterpretations” of the IPC -A-610acceptance criteria. These misinterpretations can cost your company time, money, and even yourreputation for quality. In this video we’re going to explain some of these misperceptions, to makesure that your company doesn’t fall prey to: The Common inspection errors of the IPC-A-610.lme in the morning.NARRATORWithout an industry standard like IPC-A-610, each company would be using an internalspecification. Our industry would not have a common language and the consistent criteriarequired to properly evaluate electronic assemblies. Incorrect evaluation can result in loss ofrevenue. Over inspection – or incomplete inspection is also expensive. Consider two differentinspectors. One inspector is too lenient, and lets defective product go out the door. Later it failsand now the product must be returned for repair. The cost to return the product, the repairs madeto fix the product, and the cost to re-ship the product back to the customer can be expensive, notto mention losing reputation -- and even customers. Another inspector is too strict. Overinspection is a common way companies spend money unnecessarily. The inspector asking forrework often doesn’t see or think about the cost. By having an industry consensus workmanshipstandard, we can have a common language between assemblers, inspectors, and customers.Following the IPC-A-610 correctly and avoiding the most common inspection errors will saveyour company time and money.1

DVD-71C TranscriptThe common misinterpretations that we’ll be covering in this video include: inspector‘sresponsibilities; identifying board sides; electrical clearance; wetting angles; vertical fill ofthrough hole solder; through hole part clearance; gull wing leads; bottom terminationcomponents; measling; and billboarding.Inspector’s ResponsibilitiesLet’s begin with inspector’s responsibilities. A serious mistake can occur when an inspectorevaluates an assembly with excellent solder joints -- and identifies them as Class 3 solder joints.The reality of this situation is that the customer determines the class of product your company isbuilding. The inspector only applies the acceptance criteria. A solder joint that barely meets theminimum acceptance requirements for an mp3 player would definitely be undesirable for a lifesupport system. As you know, electronic products are divided into three classes – depending onthe ultimate use; the life expectancy; and the operating environment of the electronic assembly.Let’s review these classes of products.Class 1 refers to general electronic products – which include consumer electronics such astelevisions, stereos and video games. Class 2 includes high-end computers, telephone controlsystems and other commercial equipment that falls into the category of dedicated serviceelectronic products. The Class 3 category is for high performance electronic products –equipment with high reliability applications such as military, aerospace and life- support systems.The customer specifies the class your company will be building to and the inspector has theresponsibility to determine the four levels of acceptance for the solder joint – based upon the classthe customer has chosen. These four levels are target, acceptable, process indicator and defect.The target solder joint is close to perfect – the most desirable condition – but not alwaysachievable. An acceptable solder joint is not necessarily perfect, but provides a satisfactorymechanical and electrical connection to operate properly. A process indicator identifies acharacteristic that does not negatively affect form, fit or function of a product. It is not a defect.The solder connection will work fine and be reliable. A process indicator tells you that there is anopportunity for improvement in the quality of your solder joints – and other elements of thecompleted assembly. The process indicator usually points to a difficulty in the process thatshould be remedied. The process can include machine adjustments, product design, defectivecomponents and training needed. Finally, a defect does affect form, fit or function and willrequire rework, repair or even scrapping the assembly.The problem with applying class 1 acceptance criteria to class 3 products is obvious. However,applying class 3 criteria to class 1 products make the class 1 products much more expensive tomanufacture. As you can imagine, it could be a time consuming and expensive mistake for aninspector to ask for rework of a solder joint that did not need to be reworked based on class ofproduct. And that mistake can also add unwanted heat to the circuit board causing internaldamage.2

DVD-71C TranscriptIdentifying Board SidesThe customer specifies the class your company will be building to and the inspector has theresponsibility to determine the four levels of acceptance for the solder joint – based upon the classthe customer has chosen. These four levels are target, acceptable, process indicator and defect.The IPC-A-610 has expanded the terminology. For example, board sides for through holeassemblies are called the solder source side and solder destination side -- but have no meaningfor surface mount assemblies. Solder source refers to where the solder is applied and solderdestination refers to the side of the board where the through hole components can be seen.For surface mount assemblies, we identify the primary and secondary sides of the board. Theprimary side is usually the side of the board that contains the most complex, or the highest numberof components. The secondary side of a surface mount assembly has the less complex or lowestnumber of components.When referring to the two sides of the circuit board assembly, it’s important to understand anduse the correct terminology so there are no misunderstandings. That’s because many A-610inspection criteria are specific to one side of the board or the other. If there’s confusion over theside of the board, an inspector can easily turn to the wrong page and get the wrong answer.For example, the criteria regarding land coverage for a through hole solder joint relatesspecifically to the solder source side of the circuit board. Examining the A-610, we see that landson the solder source side need some percentage of wetting to be acceptable – and that the landarea on the solder destination side does not need to be wetted. If we switched – and applied thesolder destination criteria to the solder source side, then we would be allowing defects through.Electrical ClearanceNow, let’s take a look at a common difficulty that occurs when inspecting for electricalclearance. Minimum electrical clearance is defined in the applicable design standard or on theapproved documentation for the assembly. If there is a question, Table 6.1 in Appendix A of theA-610 contains the specific information that can be used to determine whether the electricalclearance of conductors is acceptable or in violation. Some inspectors refer to an unacceptableelectrical clearance as a VMEC – which stands for violating minimum electrical clearance.Understanding minimum electrical clearance can be tricky because it’s based on how muchvoltage is generated between conductors. Be sure to refer to Appendix A for specificmeasurements.For example, any two uncoated, or electrically non-common through hole leads – protruding fromthe solder source side may be clinched too close to one another. A VMEC condition may resultin a short circuit, arc – or signal crosstalk. Category A6 in table 6.1 lists the minimum electricalclearances between conductors based upon the peak voltages specified in the left hand column.Those peak voltages are usually called out in the customer documentation. If you have anyquestions about peak voltages or on how to use this table, ask your supervisor or trainer.3

DVD-71C TranscriptWetting AnglesNow let’s discuss wetting angles. How do you recognize an acceptable solder joint? There areacceptance guidelines, but there are also exceptions. Wetting is the most important characteristicof a solder connection. Wetting is defined as the formation of a relatively uniform, smooth,unbroken and adherent film of solder metallurgically bonded to a basis metal.Misinterpreting the requirements of an acceptable solder joint can affect a company’s bottom line.Excessive rework not only causes delays, but also costs our industry millions of dollars. Justbecause a solder joint doesn’t look pretty isn’t justification for recommending rework.Various degrees of wetting are characterized by the wetting angle, or angle of contact betweenthe solder and the basis metal. A smaller contact angle between the two surfaces is a generalindication of better wetting and a stronger bond. Larger contact angles can be an indication ofreduced strength, and may indicate the use of excess solder – which is often not a defect. Also,keep in mind that lead free solder may typically have a greater contact angle than tin lead solder.On any type of solder joint, the target wetting angle is 90 degrees or less. A contact angle thatexceeds 90 degrees usually indicates poor wetting, or excessive solder. If a solder joint has aconvex appearance as a result of excessive solder, it is still acceptable if it covers all of the metalland, or pad – and doesn’t curl underneath itself leaving exposed land area visible. Convex filletscaused by excess solder extending over the land – are an acceptable condition if the solderextends to the full length of the solderable land surface.Figure 5-1 of the IPC-A-610 illustrates four wetting angles. The text says that the wetting angleof a solder joint shall not exceed 90 degrees. As you can see, example A shows a wetting angleof less than 90 degrees and we love that because that’s the target. Example B is also fine sinceit’s exactly 90 degrees. Examples C and D are also acceptable – but are an exception to the rule.That’s because they are both greater than 90 degrees. Connections exceeding 90 degrees can beacceptable when the solder contour extends over the edge of the solderable termination or solderresist due to the quantity of solder. Asking for rework on these acceptable connections is a wasteof time and money.On the other hand, that exception to the rule would not include the example shown in Figure 5-18. In this case, we have a non-wetting condition on most of the land that makes this solder jointa defect – even though it contains similar wetting angle characteristics as shown in examples Band D of Figure 5-1.4

DVD-71C TranscriptVertical Fill of Through Hole SolderNext, let’s turn our attention to through hole solder – specifically the criteria for vertical fill ofsolder inside the plated through hole. To evaluate this condition we must look at the solder jointfrom both the component and the solder sides. We've seen that the ideal or target connection hasa slightly concave, cone-shaped fillet that rises from the outer edge of the land to the componentlead. But the solder joints you see every day may not always live up to this ideal. One commonvariation of the fillet's shape is a slight dip into the through-hole – before the fillet rises onto thelead. This condition is especially common on the solder destination side of wave soldered boards– since gravity can cause the solder to sag slightly into the hole as it solidifies. As long as thesolder joint meets all the other requirements for acceptance, some amount of solder depression isallowed.A maximum of 25% solder depression, on either the solder destination or solder source side, ispermitted. This means that a minimum of three quarters of the barrel must be filled with solder.Some inspectors have a tendency to ask for rework whenever there is less than 100% vertical fill.Ignoring vertical fill or not understanding that 100% is not needed can be costly. It’s important toapply the correct amount of vertical fill to the class of product that you are building. Section7.3.5.1 of the A-610 is the place to go. As you can see, Figures 7-88 through 7-91 provide thecriteria. Notice that for class 2, 50% vertical fill is acceptable – when there is a thermal heat sinkplane surrounding the plated through hole.Through Hole Part ClearanceThrough hole part clearance is another inspection criteria that causes confusion. Again, overinspection, or the lack of it – is expensive. Part clearance is defined as the space between thebottom of a through hole component and the top of the board. But what is the true minimum andmaximum clearance? The answer is not in the “Acceptable” criteria, but often in the “ProcessIndicator” requirements.For example, let’s look at axial lead, vertically inserted components. Even though Table 7-2states there is a minimum amount allowed for component to land clearance, you will notice it isa process indicator – when the clearance is less than the minimum specified as acceptable – inTable 7-2. It’s also a process indicator when the clearance is greater than the maximum --specified in Table 7-2. In this situation, these process indicators are completely shippable – evenwhen there’s no clearance at all. Once again, misunderstanding or misinterpreting the criteria is apossible source of unnecessary rework. That’s why it’s so important to carefully read all of theacceptance criteria in the A-610.5

DVD-71C TranscriptGull Wing LeadsAt this point, we’ll take a look at some common misunderstandings associated with surfacemount – gull wing leads. Misidentifying gull wing leads can cause the inspector to apply thewrong rules to the component they are inspecting. The general inspection criteria is dependent onwhether the gull wing lead has a long foot or a short foot. For example, If there is a long footlength – meaning that “L” is equal to or greater than three lead, or toe widths – the side jointlength should be a minimum of three lead widths, or 75% of the foot length, whichever is longer.If there is a short foot length – meaning that “L” is less than three lead, or toe widths, theminimum side joint length is 100% of the foot length.There are also different rules for the low profile leads found on SOICs and SOTs; and the highprofile leads found on QFPs. In addition, heel fillets for gull wing leads provide the mostimportant electrical and mechanical connection. Therefore, care must be taken to make sure thatthe heel fillet is the proper height. The fillet height may extend to the top bend of the lead, orknee, but should not touch the component body or end seal as a maximum fillet height. As anexception to this rule, solder may touch the body of plastic SOIC or SOT components. If youoverlook this exception, you may ask for unnecessary rework – thereby creating extra operatingcosts for your company.Bottom Termination ComponentsNow that we’ve discussed gull wing leads, let’s examine another category of surface mountcomponents called bottom termination components, or BTCs. Misunderstanding these new parts,or the new grouping of many older parts can be a cause for misapplying the 610 standards.Examples of BTCs include Dual Flat No-Leads, or DFNs; Quad Flat No-Leads, or QFNs; andLeadless Chip Carriers, or LCCs. There are other types of leadless components that don’t fallinto the BTC category. For example, array style components, such as ball grid arrays, or BGAs,have their own acceptance requirements.It’s important to apply the dimensional criteria specified in Table 8-15 for Bottom TerminationComponents. Figure 8-170 illustrates the heel and toe dimensions for BTCs. Dimension Cdefines the minimum end joint width. Notice that the minimum end joint width is 50 percent ofthe termination width for class 1 – and 75 percent of the termination width for classes 2 and 3.MeaslingNow, let’s take a look at how measling can be misunderstood. It’s not uncommon for aninspector to examine measling on the circuit board and to identify it as a defect. After all,measles can be pretty ugly. Measling occurs in laminated base material when the glass fibers areseparated from the resin at the weave intersection. This condition appears as discrete white spotsor crosses below the surface of the base material, and is usually related to thermally inducedstress.6

DVD-71C TranscriptWhat’s important to be aware of is there is no defect condition for measling – no matter howunattractive it is. Even when measled areas in laminate substrates exceed 50 percent of thephysical spacing between internal conductors, it is still a process indicator for class 3 and theproduct can be shipped.There are other laminate conditions – such as blistering and delamination – that do have defectivecriteria. You’ll need to be able to distinguish between the various laminate conditions you mayencounter.BillboardingOur last common inspection error has to do with billboarding. Billboarding occurs when asurface mount chip component is mounted on its side – rather than on the bottom of thecomponent. Billboarding can be confused with tombstoning – which is always a defect.Treating billboarding as an instant defect can be an unnecessary rework expense. Billboarding isnot an automatic acceptance condition either. If you carefully follow the criteria for acceptabilityin paragraph 8.3.2.9.1, then billboarding is allowed and is a totally acceptable electrical andmechanical connection.SummaryThis program has presented the most common inspection errors – when using the IPC-A-610 foracceptance criteria. We discussed the inspector’s responsibilities; properly identifying boardsides; electrical clearance; wetting angles; vertical fill of through hole solder; through hole partclearance; gull wing leads; bottom termination components; measling; and billboarding.The more familiar you become with the terminology and the acceptance criteria of the IPC-A-610– the more successful you’ll be in accurately determining whether a circuit board assemblyshould be shipped to the customer or whether the assembly requires rework. That determinationcan make a big difference in the quality of the product you produce and the profitability of yourcompany. Those ingredients make it a win-win situation for everyone involved.7