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Author Archives: Mike
Off to the Races: Creating Winning Finishes
As promised, we are off to the races, untangling the convoluted subject of PCB surface finishes. This is a complicated subject, so bear with me as I try to break it down into bite-sized, manageable portions! This week I will discuss each available surface finish and the pros and cons of each one. Below is my version of SparkNotes for surface finishes:
PCB Surface Finish Comparison Chart
|
HASL Tin/Lead |
HASL (Lead-free) |
ENIG |
Immersion Silver |
Immersion Tin |
ENEPIG |
Electrolytic Nickel-(Hard or Soft)Gold |
|
|
RoHS Compliant |
No |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
|
Fabrication Costs |
Low |
Low |
Med |
Med |
Med |
High |
High |
|
Shelf Life |
1 Year |
1 Year |
1 Year |
9-12 Months |
9-12 Months |
1 Year |
1 Year |
|
Themal Excursions In Assembly |
Multi |
Multi |
Multi |
Multi |
Multi |
Multi |
Multi |
|
Wire Bonding |
No |
No |
Yes/No |
Yes/No |
No |
Yes |
Yes |
|
Low Resistance/High Speed |
No |
No |
No |
Yes |
No |
Yes |
Yes |
|
Soundness of Solder Joints |
Excellent |
Good |
Good |
Excellent |
Good |
Good |
Good |
|
Coplanarity |
Poor |
Good |
Good |
Excellent |
Excellent |
Excellent |
Excellent |
|
Wettability |
Excellent |
Good |
Good |
Excellent |
Good |
Good |
Good |
As I mentioned in my previous blog post, many designers working with high speed digital, RF or Microwave applications are using ENIG, ENEPIG and Electrolytic Hard or Soft gold these days. From the chart above, you can see why; these finishes offer many desired properties. However, if wire bonding is required, the field is narrowed to Immersion Silver, ENEPIG, and Electrolytic gold. Here at Transline we are often asked what the difference is between hard and soft gold: quite simply it is the purity of the gold; the purer the gold, the softer the finish. Among all finishes widely available, silver has the best conductivity.
The Tradeoffs
Many engineers and designers report significant signal loss from the nickel that is plated beneath all gold applications. As the desire for greater speeds increase, many are looking for ways to eliminate, or reduce loss due to undesirable resistivity from plating finishes. In the plating process, gold cannot be plated directly over copper for a couple of reasons. First of all, some copper gets chemically dissolved into the plating tanks, tainting the gold purity and the very costly gold bath. Secondly, on the board surface the copper and gold become diffused and mingled not allowing the gold to plate over the top of the copper. Nickel, therefore, is applied over the copper to act as a barrier to prevent these two undesirable effects. It is for this reason that many are looking to ENEPIG (Electroless Nickel, Electroless Palladium, and Immersion Gold). The Palladium is far less resistive, and due to the “skin effect,” the signal travels to the outermost areas of the circuit—through the low resistive Palladium and Gold. The only downfall for this finish is that it is more costly, and may or may not take more time since most PCB suppliers do not have palladium tanks in their facilities, and rely on outside plating services.
With greater frequency, designers are turning to Immersion silver. The drawbacks to Immersion Silver include the inability for fine wire bonding and oxidation. Oxidation can be avoided or delayed by packaging with sulfur-free packaging materials and storing in temperatures less than 95 degrees Fahrenheit. Some mild oxidation can be easily cleaned away. Any unused boards should be resealed for proper storage.
Conclusion
As you can see, plating finishes offer a series of tradeoffs in cost, performance and function. Each designer needs to carefully consider the requirements that are unique to a given project or application. I hope this information helps to clarify what the general pros and cons are of the various surface finishes available.
Next Installment
Next time, I will dig a bit deeper into this subject and discuss the impact of copper smoothness and “skin effect” and how each may help you make decisions about the surface finish. Thanks to all of you who sent me emails and questions on this subject! Keep the comments and questions coming here, or to my email: [email protected]
Further reading:
www.taconic-add.com/pdf/technicalarticles–effectsofsurfacefinish.pdf
www.ddmconsulting.com/Design_Guides/hasl_alt.pdf
— Judy
An Early Spring?
The second half of 2011 is behind us, literally and figuratively.
2011 roared out of the starting blocks before veering off the recovery path beginning in the late summer or early fall. Around November, many forecasters were predicting the doldrums to remain through summer 2012. (Some are hewing this line.)
It looks like the industry wasn’t listening. Green shoots were already beginning to emerge, some forced to the surface by one-time events like the Thailand flooding, but others due to pent-up demand by consumers and businesses.
Several large and mid-tier EMS companies, including MFlex, Flextronics, CTS, Viasystems and Key Tronic have reported December quarter revenues that topped previous expectations. Component manufacturers and foundries like Vishay and UMC are calling a bottom. Broader manufacturing indices are looking better.
I think there remains a considerable amount of inventory in the chain, but much of this is held at distributors. Thus, models that heavily weight component manufacturer revenues are going to be a bit off while the rest of the chain works through their inventory conditions. But demand down the line is improving, and I think come this time next year, we will look at the September 2011 period as the trough.
Upcoming Chats
SMT process consultant Phil Zarrow’s moderated chat is today at 2pm Eastern.
You don’t need to make the live session in order to ask a question: questions may be submitted in advance.
Future chats will cover data transfer, PCB cleaning, environmental regulations and MSDS tracking, and on March 2 yours truly will take questions on this year’s Apex trade show.
Money Talks
Designers, start checking your in-boxes for the annual PCD&F Salary Survey. In the next few days an email from UP Media will be go out containing the link to the survey.
Let me know if you don’t get the survey; we really want your input.
Chatting It Up
Fresh off the success of our premiere PCB Chat, we have quite a few more planned.
Tomorrow (Feb. 7), SMT process consultant Phil Zarrow will take your questions. Designers may remember Phil from some of the past PCB West and PCB East conferences, where he spoke on DfM/DfA.
Next week we will host the IPC-2581 Consortium, taking questions on the new data transfer standard.
On March 2, yours truly will discuss the IPC Apex Expo trade show.
We begin accepting questions for the chats a few days early, so don’t worry if you can’t make the live event. Transcripts are available in real-time and after, too.
Chatting Away
We had a great premiere of PCB Chat last week. Eric Bogatin, the signal integrity guru, hosted the nearly two hour session, answering more than 20 questions.
The transcript can be seen here (you must be signed in to Printed Circuit University to view it; registration is free).
The next chat will be Feb. 7 with SMT process consultant Phil Zarrow. Note that you don’t need to make the live session in order to ask a question: questions may be submitted in advance.
If you have recommendations for future moderators, drop me a line or post in the comments. Thanks!
Fall of Milan
Those familiar with their Sanmina-SCI history might recall the name Milan Mandari?. Mandari? cofounded the firm along with Jure Sola in 1980.
Sola, of course, remains in charge. For his part, Mandari? moved to England, bought a soccer team, and continued to invest in new businesses.
Perhaps he should have stayed in PCBs. Mandari? is currently on trial, charged with making bribes in order to avoid business transaction taxes. (He denies the charges.)
PCB Chat Premieres
We had a great premiere of PCB Chat yesterday. Eric Bogatin, the signal integrity guru, hosted the nearly two hour session, answering more than 20 questions.
The transcript can be seen here (you must be signed in to Printed Circuit University to view it; registration is free).
The next chat will be Feb. 7 with SMT process consultant Phil Zarrow. Note that you don’t need to make the live session in order to ask a question: questions may be submitted in advance.
If you have recommendations for future moderators, drop me a line or post in the comments. Thanks!
Can Cook Take the Heat?
CEO Tim Cook has taken to the Apple airwaves, rebutting claims made by The New York Times and others that company indirectly contributes to worker abuse but not rejecting Foxconn as a supplier.
In a letter, published yesterday by 9to5mac, Cook wrote, “Every year we inspect more factories, raising the bar for our partners and going deeper into the supply chain. As we reported earlier this month, we’ve made a great deal of progress and improved conditions for hundreds of thousands of workers. We know of no one in our industry doing as much as we are, in as many places, touching as many people.”
I’ll address the second point first. It’s true Apple has been singled out for bad corporate behavior toward Third World workers, while companies such as Dell and H-P are equally reliant on their supply chains (often the same suppliers), yet receive far less flak. It says here Apple is getting the brunt of bad publicity for good reason. The company has struck a wholly sanctimonious tone toward those who dared criticize its leadership. It has been strident in its support of Foxconn, the biggest (in size and in number of incidents) purveyor of recorded worker abuses. Apple on any given day is the largest (by market capitalization) company in the world. If a critic wants to make a point at a company’s expense, who better than Apple? Frankly, HP and Dell have been so beset by internal management problems, attacking them for supply-chain problems seems somewhat quaint by comparison.
As for the first point (“Every year we inspect more factories, raising the bar for our partners and going deeper into the supply chain.”), the truth is Apple does not visit every one of its suppliers every year. In 2011, Apple conducted 229 audits, 100 of which were first-time audits. According to the company, 97% of Apple’s procurement expenses are from 156 vendors. Incredibly, by Apple’s own admission, the logic says it audited many of its suppliers for the first time in 2011. (Either that, or the math isn’t working out, unless Apple is churning its supply base — composed primarily of well-known companies in their respective fields — with great rapidity, or that supply base is adding new plants with even greater rapidity, because the number of first-time audits has been at or over 100 three years running.)
I commend Apple for bringing some degree of transparency to the issue. But the numbers don’t quite add up. Nor does the nagging feeling that Apple, which perhaps has no parallel when it comes to leveraging a supply chain for competitive advantage, could effect positive change at places like Foxconn and Pegatron, if only it were willing to shoulder the financial risk.
When you have $100 billion* in the bank, you can afford to stop by each of your suppliers at least once a year. And when you’re the biggest company in the world, and apparently comfortable lecturing anyone else on what they should think, then you’d better be able to handle the blowback. If Cook can’t handle the heat, he should get out of the kitchen.