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Dr. Craig D. Hillman
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CEO & Managing Partner
DfR Solutions
Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.

Dr. Craig D. Hillman has submitted responses to the following questions.
Reliability Concerns When Converting to Lead-free
Don't do it. Previous work has demonstrated serious issues when mixing SnPb HASL with SAC305 solder. ...
QFN Test Failures Caused by Flux
Absolutely. ...
Can a Few Contaminated Joints Cause an Assembly to Fail RoHS Compliance?
1000 ppm is only for unintentional contamination. If the joints were deliberately retouched with SnPb, the acceptable level is 0 ...
Estimating Failure Rate During Rework
As a general rule of thumb, there is a 10X jump in defect creation between each assembly process. SMT Reflow ...
Gold Plating and Embrittlement
To the best of my knowledge, gold plating in electronics at the package or assembly level is still not applied ...
Class 3 Pin Contact Question
This will either not be a problem, accelerate fretting behavior or introduce a cold weld with a high resistance due ...
Very Low Temp PCBs
Application-specific. If the product will just sit there and not be subjected to any changes in temperature or mechanical loads, ...
Circuit Board Bow and Twist
A three-zone oven? Wha?? That seems crazy in terms of being able to control a repeatable reflow process. If the ...
Solder Mask Ghosting
Best practice is to thermally cure with a UV bump. You can quickly assess degree of solder mask cure through ...
Suggested Limit for PCBA Heat Cycles
Most enterprise and telecom companies require the ability to withstand six thermal cycles (two reflows, wave, and three reworks). Note, ...
Question About SN100 Solder
Both DfR Solutions and iNEMI have published data on SN100C performance. For the most part, it falls in between SAC305 ...
BGA Joint Voids - Accept or Reject
Too many voids at the interface. Single voids in the bulk of the solder play little role in time to ...
Removal of Non-functional Pads from Inner Layers
Non-functional pads should be removed if this is a signal via. Non-functional pads do not improve reliability from a barrel ...
ESD and Humidification
Companies that are highly sensitive to ESD will typically require a minimum of 30 to 40%RH, regardless of ESD protection.  ...
What is Causing Laminate Cracks?
Most thermal stress test requirements called out by IPC actually require some moisture pre-conditioning. So, I would tend to lean ...
BGA Reflow on HASL PCBs
Yes. Several PC manufacturers are using Lead-Free HASL ...
Can Solder Joint Geometry Change Resistance?
More than likely you have an increase in surface leakage. ...
Lead-free Components in a Leaded Process
For leaded parts, no problem (note, do not use 'lead' for Pb as 'lead' can also mean a part with ...
ENIG and Black Pad
You likely have a sulfur contamination issue. Sulfur residues can occur when there is ineffective cleaning after the nickel plating ...
Puzzling PCB Reflow Delamination Problem
HAL is much less stressful than SMT. Problems with board lamination can show up in SMT and be fine in ...
Laminate Glass Transition Change
Depends on board size, board thickness, and reflow peak temperature. Cell phones can easily be assembled with 150 Tg laminate. ...
Soldermask Insulation Issue
No. Solder masks are not designed as dielectric insulators. ...
Can Water be Harmful to Electronics Components?
I would not be too thrilled with a process that cleans with ordinary soap. A special saponifier is more appropriate. ...
Cleaning No-Clean Solder Paste
The no-clean flux must be compatible with the no-clean cleaner. The white spots suggest otherwise. Talk to your no-clean paste ...
Cause of Unusual Contamination?
Pore corrosion. I assume this is gold over nickel plating structure. Depending upon the duration, could indicate elevated levels of ...
Thermal cycle limit
You are mixing and matching terminologies. Class 3 is a manufacturing specification. Thermal cycling has nothing to do with manufacturing. ...
Reflow Solder Process Issue
Why do you believe it is related to temperature uniformity? Typical drivers for solder robbing is overprinting or slump of ...
BGA Rework
Sense can mean different things to different people. The criticality of solder paste height increases as the size of the ...
Determining Current Carrying Capacity
Check out IPC-2152. ...
Voiding after under-fill
The primary tool for this activity would be acoustic microscopy. There are primarily two companies in this space: Sonix and ...
Lead Float
How big is the die in the TSOP? A number of companies are reporting issues with this kind of behavior ...
Cause of BGA Solder Joint Bridging
Take a methodical approach. First, look at the board bond pads. Board shops often (too often) make changes in the ...
Lead Free Surface Finish
There is limited data on shelf life for SAC HASL I would recommend you use the IPC steam aging test ...
Tg and Td for lead free process
Requirements are primarily driven by peak temperature, which is driven by component and board size / thickness / complexity. With ...
Resistivity and Cleaning
Typical DI equipment tends to create DI water with resistivity of 2 to 5 megaohms. Resistivity greater than 10 megaohms ...
The Role of Formic Acid
Formic acid is one of the weak organic acids that can be used in no-clean formulations to prepare the conductor ...
Ultrasonic cleaning PCB's after wave solder
The component temperatures should be 60C or below before contact with water. Otherwise, cracking of components can occur. ...
Conformal Coating Specification Violation
I don't understand the question. To avoid conformal coating? To avoid touching conformally coated components? Needs clarification. ...
Scribe lines for depaneling boards
The specifications tend to be based on the web thickness (board remaining) rather then the depth of the scribe lines. ...
Intermetallic Spalling
Spalling typically refers to delamination of a surface layer with some degree of curvature. I have not heard that term ...
Acceptable "reject rate" for hand assembly
Typical first pass yield on hand assembly is 5000 ppm. ...
SMT adhesive problems after wave solder process
I would immediately suspect board cleanliness. Are the parts falling off with or without the glue? If it is glue ...
Difference between ENIG and Flash?
You are comparing apples to oranges. ENIG describes materials (nickel and gold) and processes (electroless for nickel and immersion for ...
Socketed IC's
Insertion and retention force should be specified. You should also control the spring material to make sure that stress relaxation ...
Tin Whiskers
Unfortunately, your terminology is slightly confusing. Tin whiskers can penetrate paralyene. On the other hand, if the interface is weak, ...
Cleaning tin-lead and lead-free boards
I think the cleaning guys will say no, but you can run a number of tests to confirm the effectiveness ...
Rigid and flex board assembly
It seems like you are stating that you are having tearing of the flex circuit at the interface with the ...
Lead-free bar solder for wave soldering
At this time, the solder with increasing market share in wave applications is tin-nickel-copper, such as SN100C from Nihon Superior. ...
Wave solder and reflow 0805 capacitors and resistors
Can you select a pallet to prevent the SMT parts from being hit by the wave solder? The resistors should ...
HASL PCB's compared to OSP?
I assume you are inquiring about Pb-free HASL. The biggest concerns are damage to the board and uniformity of thickness. ...
Baking lead-free and lead PCB's before assembly
They should be on trays. Make sure the trays are low outgassing and can survive the temperature of the baking ...
Small component rework
Irons are easier than tweezers? This is contradictory to my experience, but the end results should be about the same. ...
Cleaning PCB Boards
Depends on the solution. Some window cleaners are primarily alcohols; others contain a significant amount of weak organic acids. The ...
Double sided SMT
Design the board so that heavy components (power components, large BGAs, etc.) are on one side (the second side). Make ...
Reflow and wave soldering OSP Boards
This is a common issue with Pb-free solder. For the most part, it depends upon your environment and your level ...
Oxidation on plated through holes
Plated through holes for screws? Or plated through holes as attachment points? If I understand your issue, you use the ...
Lead levels in lead-free process
The introduction of lead does not, in of itself, reduce the inherent strength of the solder joint. The primary concern ...
0805 vs. 0603 availability
Good question. Numerous studies have shown 0805 trending towards obsolescence. Of course, by the same token, through hole components went ...
Proper method to bake PCB's
They should be on trays. Make sure the trays are low outgassing and can survive the temperature of the baking ...
Copper Dissolution issue
According to studies at Celestica and other organizations, you've got approximately 25 to 30 seconds of exposure. Wave soldering should ...
Reflow oven profilers
Benchmark yourself. What does ok mean? What is your first-pass yield? What is your DPMO? Is it up to industry ...
Remove and replace a 240 pin connector
Most companies use either hot air / solder tip with a vacuum or a solder fountain. The concern is rarely ...
Aqueous Cleaning Process
I don't like localized cleaning. If there is an intensive need to perform a soldering operation after aqueous cleaning, we ...
Removing oxidation from partially assembled boards
Try increasing solder pot temperature and going to a more aggressive flux formulation (maybe moving from a no-clean to an ...
Help debugging wetting problems
Wetting issues are driven by board, solder, component interactions. Your letter seems to suggest solderability issues across the board, so ...
RoHS tantalum capacitors burning during functional test
You may be experiencing popcorning of your tantalum capacitors. We have observed this with several of our clients. Visually inspect ...
Small hole via plating reliability
Plating reliability tends to be a function of hole size only with the respect to aspect ratio (board thickness/hole diameter). ...
Coating to stop tin whisker growth?
There is no conformal coating that will stop a tin whisker from emanating from a tin-plated surface. However, it has ...
RoHS exemption for agricultural equipment in Europe
Automotive/transportation is not one of the 10 categories under the RoHS Directive. A more appropriate place to look for material ...
Regarding lead free, can I use the reflow ovens I currently have in production?
You will have to ask Heller and Vitronics. One of the problems with older ovens is that they can reach ...
Average Temperature/Humidity for an Electronics Assembly Facility?
Humidity levels should be maintained around 60%RH. Too low and you have ESD issues (think winter time). Too high and ...
Pre-wash boards prior to conformal coating
Ah, the typical conflict of no-clean versus conformal coating. As a general rule of thumb, I am against putting down ...
Concerned about "tin pest"
The best tin pest studies recently are by Bev Christian of Research in Motion and Keith Sweatman of Nihon Superior. ...
RoHS compliance for SMT and Through-hole equipment
Stationary industrial equipment are exempt under the RoHS legislation. If, for some reason, your equipment fell under the auspices of ...
AOI or X-Ray inspection?
Depends on a number of factors, including Do you have area array devices (BGA, CSP)? Are most of your soldering ...
Failure at the ENIG finish on the BGA substrate
We are dealing with a similar issue at this time. Most BGAs are electrolytic nickel/immersion gold, but sometimes you have ...
Is it possible to run Pb-Free reflow without nitrogen?
It is possible, but it could also be cost effective to use nitrogen. Depending upon your resources and time, it ...
Since we build to customer spec are we safe from Material Declaration?
Per the RoHS legislation, the CM is not responsible for ensuring compliance of the entire. This is the OEM's responsibility. ...
What alloy do you recommended for filters used with SAC305?
High lead (>85%) solders are still exempt under the RoHS legislation. This has been the choice of most companies building ...
Problems with defect BGA connections on large BGA's and on ENIG plated boards
The industry is starting to recognize this as a systematic problem. For reasons currently unknown, BGAs assembled to ENIG-plated boards ...
RoHS existing products vs. new products
Nope. New in the RoHS Directive as in "from 1 July 2006, new electrical and electronic equipment put on the ...
Standard pricing or estimating book for PCB design services
Really depends. The problem with correlating this with buying a car is that cars come with most of the "options" ...
Can PCB's designed for Sn/Pb be used in a Pb free assembly?
General rules of thumb: No real design changes are required when moving from SnPb to Pb-free. Material changes may be ...