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Leo Lambert
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Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

Leo Lambert has submitted responses to the following questions.
Insufficient Barrel Fill on Through-hole Components
Plated Through Hole Barrel Fill with lead-free solder and low solid content flux. Although the thickness of the board and ...
Cleaning Under Low Clearance Components
The use of a low-solid no clean flux when used properly, i.e., correct profile and reflow cycle, the residues will ...
What Caused SMT Pads to Oxidize After Reflow
One would have to question the porosity and thickness of the gold immersion plating. Beneath the gold plating is a ...
Specific Solder To Control Dendritic Growth
Dendritic growth or electromigration of conductive surfaces is based upon the conductivity of the laminate material and the contaminant on ...
What Is Causing Slanted Pins After Reflow
The Pogo pins appear to be surface mounted and once the solder reflows and expands the components or pins will ...
IPC-A-610 Class 3 - IPC-A-600 Class 2
No, No, No. If the contract states the product is to be inspected to IPC-A-610 Class 3, then that is ...
Two Year Component Date Code Mandate
Date codes, dates of expiration, used by dates, shelf live, what do they all mean? J-STD-002 and J-STD-003 discuss plating ...
What Is This Contamination?
This looks like some form of corrosion. Most likely this was cause by flux residues beneath the coating. Any applied ...
Frequency of Temperature and Relative Humidity Tracking
There is no form on how often this should be done, but I would think the systems can continuously monitor ...
Solder Paste Thickness Measurements
Since your PCBs are approximately 10" x 10", I would measure three on each side, then I would check the ...
Reliability Concerns When Converting to Lead-free
I wish it was as simple as converting from one alloy to the next. It is not! Couple of quick ...
What Is Causing Connectors to Bow?
I would think this is due to thermal expansion of the connector. With no restrictions visible changes are minimal and ...
Is Solder Mask Considered an Insulator
If solder from a PTH lead, on the source side, touches solder mask that is over a copper ground plane, ...
Stainless Steel Benches and ESD
I'm not sure I have an answer to this question and whether it requires additional questions for clarification. From a ...
Using Solder Paste Beyond the Expiration Date
The residues could be from a variety of sources and is also dependent upon the alloy of solder being used. ...
Concerns With Silver Finish Component Leads
From my understanding, the silver will go into solution and not be a problem for the strength of the joint. ...
Solder Splashes During Wave Soldering
There are a couple of issues to look at regarding the solder splashing up onto the bottom side of the ...
Requirement for Toe Fillets
This section of the IPC-A-610 document does discuss the wetting of the lead (L) and (D), the width of the ...
Problems With Large Voids
Voids causes and cures, is a popular question at many meetings. You mentioned that failures did occur but did not ...
Partially Visible or Hidden Solder Connections
The original intent of this question was to be able to check the bottom side of the solder joint to ...
Initial Screen Print Test Board
The important issue is the accuracy of the alignment of the stencil to the board. If the printer does not ...
Components Falling Off During Wave Soldering
This sounds like surface mount components which are secured with an adhesive are then sent over the wave solder system. ...
Delamination After V-cut
I would suggest reviewing IPC-4101D WAM1 Specification for Base Materials for Rigid and Multilayer Printed Boards, for the particulars of ...
Selective Soldering Frame Causing Cold Solder Joints
In my experience, cold solder joints were manually created, due to insufficient flux, insufficient heat and insufficient time to create ...
QFN Test Failures Caused by Flux
There are many inquiries regarding residual flux beneath surface mount component and from my perspective, flux qualification and thermal profiles, ...
Can a Few Contaminated Joints Cause an Assembly to Fail RoHS Compliance?
From my understanding, the weight of the lead is based upon the weight of the solder on each individual component ...
Estimating Failure Rate During Rework
I'm not sure anyone can answer this question with the information provided. Test failures were typically balanced between process defects ...
Copper Dissolution Rate
Great question on the dissolution rate: I've listed a few places where information is available for you to research. The ...
Hot Air Solder 0201s and 01005s
Thank you for the question. I understand your frustration in using hot air to reflow those small components 0201 and ...
Floor Life of MSD Parts
What needs to be defined is the moisture sensitivity levels of the components as recommended by the manufacturers. Once this ...
QFN Open Solder Joints
There are lots of variable when installing these types of components of which some are definitely more important than others. ...
Stencil Cleaning Frequency
I don't know if there is an industry standard, but common sense would seem to dictate to clean the stencils ...
Customer Approval for Repairs
Per the information provided in IPC J-STD-001 I submit the following: J-STD-001 Paragraph 1.5.1 Hardware Defects and Process Indicators, states ...
Gold Plating and Embrittlement
Gold embrittlement in solder joints has always been caused by a percentage ratio the weight of the gold versus the ...
Hand Soldering at Low Temperature
Kind of provides a new definition of cold solder joint. Two things would concern me with these conditions, thermal shock, ...
MELF Component Misalignment
Not being sure of the process, but I imagine this is all being done in a sequential fashion, with the ...
Cause of Incomplete Solder Reflow
Im not sure the exact meaning of flux exhaustion, however my interpretation is, there wasnt enough flux in the solder ...
Solder Paste Past Shelf Life
Solder paste consists of three major elements, solder powder of a give size, flux, and a viscosity agent. All three ...
Class 3 Pin Contact Question
This is a design issue and any and all design issues override the Classes of assembly as defined by IPC ...
MSD Components Baked Too Long
From a soldering perspective,  you could have some issues. Depending upon the plating on the leads and thickness of the ...
Trichloroethylene Alternative
In another life this was my life. Trichloroethylene is a Chlorocarbon material and it is a carcinogen and must not ...
Rechecking Thermal Profiles
Checking profiles on an ongoing basis is a must due to the deterioration of the equipment and the variations in ...
Soldering Station Calibration
This is a great question and we just went through this question at the last APEX show in Las Vegas. ...
PCB Outsourcing
From my perspective the top 4 or 5 items to consider for outsourcing printed circuit board assembly are the following ...
Blow Holes and Disturbed Joints
Interesting question.   It is not identified where and when the boards were baked, be it either prior to solder ...
Burned Chip Repair
The process would include the removal of the chip then subsequently the removal of the burnt laminate material. The procedures ...
Confused About IPC-A-610 Class 2 vs. Class 3
The question is confusing at best.   The inspection category to be used to inspect the product must be defined ...
Automatic Insertion Causing Plated Damage
Interesting question. Sometimes I believe the customer has to be educated and this may be the case in this situation. ...
What is a Soft Solder Joint?
According to Howard Manko, Solders and Soldering, page 142, the Joint strength of a lap solder joint is ((Length of ...
IPC-A-610 Solder Joint Acceptability Question
You state in your question:   "Our team looked at the verbiage above figure 5-1, and said that since it ...
Concerns Replacing High Speed Components with No-Clean Solder
This question comes up from time to time and I shudder at the thought that people would use a flux ...
Solder Caking to Bottom of PCBs After Wave
It is not mentioned as to what type of solder was drained from the solder pot. Was it the same ...
Selective Printing for BGA Components
Interesting question. I don't see where this would be an issue. I would check whether or not an underfill would ...
What Causes Component Rotation During Reflow?
The answer to this question could come from everywhere and I'm sure the answers provided here will be varied as ...
Extending Shelf Life for Jars of Solder Paste
Extending shelf life on solder paste may be a tricky thing to do. I would recommend the following test be ...
What is Causing Solder Joint Cracking
Manual soldering has many variable associated with the process. Training is a must to reduce many of the variables and ...
Bow and Twist Requirement
The limits of Bow and Twist have been a requirement since the initiation of the IPC documents. Historically the issue ...
Legend Marking Discoloration
I cannot think a process to prevent this from happening, other than shielding the total area around the component where ...
BGA Joint Voids - Accept or Reject?
Of all the voids I've looked at, none have shown this type of characteristics. I would ask how this solder ...
Through Hole Connector Solder Joint Hole Fill
This question is interesting from the viewpoint of the requirement of IPC-A-610 and J-STD-001.   J-STD-001 states in Section 4.18.3 ...
PoP Assembly Options
I would go with option 1, the assembly process first, putting all the components together and verifying they are ok ...
Component Shifting
Situation: Components moving or shifting from the position at which they were placed.   Most times this is related to ...
Jumper Wire Gauge
According to IPC-7721, Section on Jumper Wires, section 6.1, in the Jumper Wire Selection section #5 states: "Recommended wire is ...
Spotting After DI Water Cleaning
This appears to be some minerals which are still in the water. We had an issue similar when working for ...
Long Term Component Storage
Storing of components for a long period of time is based upon the requirements of J-Std-033C. This document specifies the ...
Trouble Soldering a PC104 Connector
I would still recommend the use of performs, however I would recommend that the math be calculated to figure out ...
What is Causing Laminate Cracks?
From what I understand this is due to the change in epoxy being used for the higher temperature laminates. With ...
Stencil Cleaning Procedure
Interesting question and wonder about what problem or problems exists by cleaning the stencils in this fashion. I imagine the ...
Unusual Solder Appearance
The appearance of the solder joint is dependent upon many variables, therefore many questions need to be asked relative to ...
Lifted Lead on SOT Component
I would imagine it is the side with the single lead that is lifting up out of the solder or ...
Class 2 vs. Class 3
This is a big answer and there are many parts to the answer. Let me start by stating there are ...
Reduced pH and Specific Gravity of Flux
By lowering the pH of the flux, it becomes more acidic and the same applies to changing the specific gravity. ...
Toe Fillet Requirements on Gull Wing Components
Per IPC-610, section 8.3.5 Flat Gull Wing Leads and section 8.3.6 Round or Flattened (coined) Gull Wing Leads, there is ...
Dross Particles Sticking to PCBs
I agree with some of the comments, but from my perspective, the solder level in the wave is too low. ...
Coating Scored Panels Prior to Separation
The only important issue to consider is the areas which are to be coated and the areas that are to ...
Solder Paste Alloy Check
If the lead-free solder paste was processed through the leaded thermal profile you may end up with unreflowed solder paste ...
Un-cleaned PCB Assemblies Potted
Interesting condition. I would think it depends upon the initial moisture in the environment prior to potting the product. If ...
Solder Popping Out of Holes
I'm not sure I've seen this, but I guess I can gamble and offer my two cents.   If the ...
Matrix for SMT Assembly Labor Costs
It has been a long time since I've done any of this, but I would suggest you consider the element ...
Test for Flux Penetration
Flux penetration is important to the flow of solder up into the plated through hole. The elements which need to ...
BGAs Mixing Tin-Lead and Lead-Free
The reflow temperature of the Lead-Free process will be high enough to melt the Tin/lead alloy and the Tin from ...
Rework for OSP Assemblies
OSP (Organic Solderability Preservative) boards have been around for many years. As to whether the rework or repair process should ...
Deionized Water Sample Testing
The De-ionized water will absorb Carbon Dioxide in the air and this will deteriorate the megohm readings of the material. ...
BGA Die and Pry Testing
I would need more information to make the determination as to whether or not these are Kirkendall voids, as Kirkendall ...
Wire Tinning Dispute
I'm not sure of the exact answer, but I would guess it probably has to do with the type of ...
Mixing Different SAC305 Solders
Based upon all the patents on solder alloys, I would doubt there would be a problem. To verify this make ...
Delamination Causing Scrap
Delamination has been a concern since the beginning printed circuit boards and increased with the introduction of multilayer boards. The ...
Package-on-Package Rework
This would all depend upon the skills of the technician doing the work. The other element I would consider is ...
Tacky Substance Under Zero Clearance Parts
There are some issues to consider, one of which is the height of the component after reflow and the ability ...
Flux Oozing from Insulated Wires
Flux oozing! Great question! Someone had to put the flux there to start with, so reviewing the tinning operation and ...
Conformal Coating in Low Humidity Environments
As far as I can tell, there is no downside to using conformal coating in a low humidity environment. I ...
White Discoloration After Ultrasonic Cleaning
I would check the compatibility of the flux to the cleaning solvent. The fluxes can be either rosin or resin ...
Fastening Surface Mounted Connectors Before or After Refow?
IPC-A-610 Section 7.1.8 Component Mounting Connectors states that when assembling the PTH connectors into the board the board locks are ...
IPC-A-610 Criteria
This response to this question could take forever; however, let me try to answer it this way. The plated through ...
Acceptance Criteria for D-Pak Components
Reference IPC-A-610 Page 8-95, Section 8.3.14 Components with Bottom Thermal Plane Terminations. The End overhang of thermal plane is not ...
Idle Wave Solder Temperature
I would recommend the system be shut down and turned on prior to the start of the shift. Automatic timers ...
Insufficient Plated Hole Fill with Electrolytic Capacitors
For the typical thickness printed circuit board, .060 and .090" boards the hole filling of the plated through holes is ...
HASL vs. Immersion Gold
This is an interesting question from the perspective of utilizing the finish solderability coating on raw boards for a protective ...
Wave Solder Pot Contaminated with Lead
My first question: How did the lead get into the solder pot? I'm not sure there is an easy way ...
Problems With Skewed D-Pak Components
The component is moving due to the surface tension of the fluid flow and density of the molten solder. My ...
Bare PCB Shelf Life
I'm sure there will be different types of answers for this question. Is the full shelf life of bare PCB's ...
Mixed Technology - Which First
This is or could be a dangerous precedent as it must be known as to whether or not the PTH ...
Unusual Component Lead Contamination
This is an interesting picture and to determine the exact cause of it would be difficult by just looking at ...
3D Solder Paste Inspection
Three D inspection systems are very common in high volume operations. This is the perfect place for automation to be ...
Defective Pads?
It appears as though there are a couple of things needing to be investigated. As stated the boards were HASL ...
Special Cleaning Needs for BGA and QFN Components
With the introduction of new components and the decreasing spacing beneath those components impacting the ability to properly clean off ...
Solder Hardness Comparison
This is an interesting question and could create a good topic for a metallurgical evaluation. I would surmise the issue ...
Devices for Soldering Iron Tip Cleaning
One of the methods we are starting to see move into the forefront for cleaning solder iron tips is the ...
Education Level Prior to IPC Certification
We are asked this question often and sometimes it is difficult to sort out the ambiguity regarding what the customer ...
Soldering Iron Tip Breakdown
This is a great question and a real problem being experienced by many users of lead-free solders. With the introduction ...
Opens at BGA Component Corner Balls
Based upon the warp and twist characteristics of the printed board laminate materials and the BGA this could be the ...
Hand Solder vs. Wave Solder
Should we or should we not upgrade to wave soldering for our products? Manual soldering is a very unique process ...
J Lead Overhang Specification
Per IPC-A-610 Rev E, page 10-44, " Although not rated for dielectric strength, and therefore not satisfying the definition of ...
Components Lifting During Wave Soldering
The forces exerted by the surface tension of the molten solder is greater than the weight of the components and ...
Soldering Quality & IPC Standard?
The criteria for lead protrusion requires the lead is visible in the solder joint as defined in Section 7.3.5 of ...
Best Way to Eliminate Dross?
The best way to reduce dross in a tin/lead solder pot is a question people have been trying to answer ...
Through Hole Component Phase Out
Back in 1980, the thought was surface mount technology was going to replace all through hole components and technology within ...
Rules for Reusing Components
Reusing components which have been removed from any printed circuit board is risky at best, due to the thermal excursion ...
Can Water be Harmful to Electronics Components?
Let me start with this quote from George Santayana. "Those who cannot learn from history are doomed to repeat it." ...
Lifted Leads on QFP
There are a few things to review, the flatness of the pads in relationship to each other, the co-planarity of ...
Solder Fillet Peaks
Solder peaks are usually caused by a few reasons such as; not enough flux, the solder iron is pulled away ...
Recommendation for PCB Surface Finish
Not knowing where this product is being used, there are many alternatives to select. The easiest one that I would ...
PCB Handling and Storage Concerns
This document is in the final stages of review, so it is difficult to determine at this point the reception ...
Cleaning No-Clean Solder Paste
I find this a politically charged question. A flux material is being used which does not need to be cleaned ...
Is Baking Required After Aqueous Cleaning?
There are many elements or variables involved before making this decision. Two of them are related to the process and ...
Which to Use - Rosin Flux or Water Soluble?
When this debate first arose, Rosin fluxes were not as aggressive as the more active water soluble fluxes. The thought ...
Class 2 vs. Class 3 Distinction
The first definition is the differences between the two classes of products where class 2 and class 3 differences are ...
SMT Component Shift
There has to be some differences in the operation of the similar equipment. I would check for the following: Conveyor ...
Which term to use, PWB or PCB?
Great question. IPC-T-50H, has a definition for each of these terms, Printed Circuit Board, provides both point-to-point connections and printed ...
Recommended lead to hole ratio
The lead to hole ratio has to consider the methodology of component insertion and whether or not intrusive reflow or ...
Alternative to Conformal Coating
Some manufacturers use epoxy to pot their products to protect them from any environmental exposure. By creating a cavity and ...
Screen Print Shelf Life
Since paste deposition or screen printing is not a critical delay time element in the process flow, I would not ...
Re-certify a reflow oven
To re-qualify or re-certify the oven and venting system, my suggestions would be to re-profile all the boards and see ...
Wave solder process issue
This question is very interesting as I've not been asked this in thirty years. Not to get into historical information ...
Cleaning No-clean Flux
You have to ask the question of How Clean is Clean? It is probably not a good practice, but will ...
Tin-lead and no-lead compatibility issues
The lead-free finish on the boards sounds like a SAC type alloy. This is a metallurgical issue which has been ...
Rework Circuits Under BGA's
Any circuits added due to repairs has to address what circuitry it is being removed or replaced. If the defective ...
Halogen Free tin lead or pb free
In this age of the EU directive, you should demand a material declaration sheet from the supplier who will identify ...
What is the correct coupon for moister and insulation test
I've dug out the test coupons for you along with their test methods. Hopefully this will clarify your questions. Test ...
Wave Soldering Problems
Insufficient hole filling and why? There are many many reasons for this and I would not know where to begin, ...
Through Hole Soldering on 24 Layer Board
Manual soldering of thick boards is a very delicate operation. Solder iron temperature, solder iron heat capacity, preheating of the ...
Recover Solder from Dross
The environmental requirements and regulations which would be imposed to initiate this kind of process within your facility may be ...
Reflow BGA's with CSP's
Unused vias should be protected from pulling the solder off BGA pads and any other pads for that matter and ...
Humidity and Corrosion
Corrosion products can come from anywhere and moisture is the element that makes it happen. My first thought without seeing ...
Best Board Cleaning Methodology
Very interesting question! Why are the solder balls there in the first place and where did they come from? Are ...
Urethane Conformal Coating Problem
My question would be where is the silicone coming from in the first place? The first thing would be to ...
Solder Components to Thin Flexible Circuits
The best way we've found to do that type of assembly is with fixturing to hold the flex in place, ...
Solder Deposits on Components During Wave Soldering
Securing components on the bottom side of the printed circuit assembly is a common practice. The chip wave was developed ...
No-Clean Flux: How much is too much?
Flux by definition is an acidic material. Any amount left behind is too much as the residual salts are always ...
Solder bridging on BGA's
Your answer is yes, all of the above. Each variable has to be taken into consideration when they are selected ...
How many zones are adequate for lead free profile
Interesting as this question is, the profile is based upon the ability of the equipment to provide enough thermal energy ...
Acceptable Number of Repairs
This question has been asked for many many years and my answer has always been the same. In the 60s ...
How much Board Baking is to much?
This is a good question but there are missing items. Why is the board being baked in the first place? ...
Lead Float
There could be a variety of reasons for this particular condition to occur with this particular type of component. There ...
Solder Paste Replenishment
Solder paste replenishment is typically based upon how the paste is performing on the stencil relative to its rheology, such ...
Zinc in solder
Zinc has always been considered a contaminant in solder. As quoted from Manko's Solders and Soldering, McGraw Hill, page ...
Part Movement During Reflow
I'm not sure I have the exact answer, but my thoughts on this are that the (weight of the component) ...
Maximum thermal stress temperatures
Typically PTH components do not get exposed to soldering temperatures. The leads and boards get exposed but the components do ...
Pros and cons of HASL, OSP and Immersion Gold
A very interesting question and the answers could go on forever. HASL ( Hot Air Solder Leveling) replaced Electroplated Tin/Lead ...
Wave soldering LCDs
I would think selective wave soldering systems or selective soldering stations would be able to handle this application quite well. ...
Component Shift During Reflow
Components may shift during reflow due their ability to float on the molten solder. Some components have many pads or ...
Coating or encapsulating tin-lead solder joints?
Thank you for an interesting question. The Surface Mount solder joints can be created using either Leaded solder or Lead-Free ...
Deflux Eutectic and Lead-Free Assemblies
Cleaning has nothing to do with the type of solder being used, whether the material is eutectic or lead-free. The ...
Control Electronic Static Discharge
All equipment should be grounded through the power cord. If any portion of the equipment is isolated from the chassis ...
Conformal Coating Specification Violation
The amount and coverage of conformal coating is and must be based upon the product design criteria. For example IPC-A-610 ...
Scribe lines for depaneling boards
The document you are looking for is IPC-2222, Sectional Design Standard for Rigid Organic Printed Boards. Page 14 Fig 5-2 ...
Wire stripping insulation prior to tinning
This is all dependent upon the manufacturing cycle and the time span between the stripping operation and either the tinning ...
SMT Epoxy for lead-free wave
The glue or epoxy used to secure components which will be wave soldered must be able to withstand the thermal ...
Any "Standards" on pad repairs?
A board needing to be repaired needs to be approved by the customer as it will not meet the requirements ...
Monitoring temperature and humidity
I just checked the web page with a search on Temperature/humidity monitoring systems. Lots of information available, but there are ...
Lead Free BGA Reflow
No it may not, as you failed to mention whether or not your HASL boards are Sn/Pb or Sn100C solder ...
Using tin-lead solder on RoHS parts
This is a backwards compatibility issue, using lead-free materials with a leaded solder. Many of the components manufactured in the ...
HASL and solder mask process?
HASL was a process to apply solder to the exposed copper on the boards, especially the pad areas and plated ...
Jumper wire guidelines
There are a number of places where this type of information is available, IPC-A-610, section 4.1.3.2 for attachment to threaded ...
Cleaning tin-lead and lead-free boards
Can the same equipment be used to clean Lead-free types of fluxes? The answer is yes, but the process parameters ...
Lead-free bar solder for wave soldering
Although I've seen many companies who have switched to lead-free soldering in their wave solder machines, I've not seen any ...
Books or Publications of today's electronics assembly
There are many books and publications which can supply the information you are looking for relative to electronic fabrication, Soldering ...
Cleaning solvent to replace Forane 141b?
Forane 141b is a substitute for Forane 113, and this is an Ozone depleting chemical and I would not recommend ...
Small component rework to IPC spec.
There is no inherent problem in using 2 soldering irons to remove chip components. Soldering tweezers are simply two irons ...
Double sided SMT
Double sided surface mount products have been manufactured for many years and the process is typically the same as it ...
Cleaning PCB Boards with window cleaner?
I would not recommend a window cleaner to remove flux residues. Window cleaners have different chemicals in them that could ...
Hand soldering skills
EPTAC Corporation has a Soldering Assessment Program which may fit this need perfectly. The program includes Instructor Guide, Kits are ...
OSP Board rework and cleaning
Boards or assemblies with OSP coatings are treated the same as any other solderable coating applied to printed circuit boards. ...
Reflow and wave soldering OSP Boards
Exposed copper around the periphery of the pads is acceptable. With the use of the new lead free solder alloys ...