Circuit Design for Reliability Part 3

Continuing the circuit reliability discussion, we will focus on the importance of component selection and board layout in this Blog. There are three major factors designers need to keep in mind while selecting the components: input bias current, input offset voltage and noise figures.

Let’s say the circuit is for audio applications and the op-amp is TL072 selected for low noise and wide bandwidth, running on supply voltages of +/-12V. The TL072 has a maximum quoted Vos of 10mV. With a gain of 1000, this will be amplified by a closed loop gain to give a dc offset at an output of 10V – which is far too close to the supply rail to leave any headroom to cope with overloads. In fact, the TL072 is likely to saturate at 9-10V anyway with +/-12V power rails.

The significance of input bias current is: it determines the steady-state input impedance of the amplifier. This low input impedance affects the performance and accuracy of the source of signal like sensors.  A perfect amplifier with perfect components would be capable of amplifying an infinitely of small signals to, say, 10V p-p with perfect resolution. The imperfection which prevents it from doing so, is called noise. The noise contribution of the amplifier circuit places a lower limit on the resolution of the desired signal, and designer will need to account for it when working with low-level (sub-millivolt) signals or when the signal-to-noise ratio needs to be high, as in precision amplifiers, audio or video circuits.

Selecting the components requires an in-depth circuit simulation and analysis with sensor model, noise values of the amplifier over bandwidth of the signal, and variation in bias current/offset voltage over temperature range. PNC’s dedicated circuit engineers are experts in circuit analysis and have been supporting Companies and Individuals across the nation.

PC Boards - Board on Board with Ventilation Tunnels

Over the past two years, we have been seeing some really innovative and high Tech PCB layouts.  One case in general, was a Board Design that incorporated multiple ventilation tunnels within the layer structure of a Board on Board application.  What is Board on board?  The application was to mount 4 pieces of laminate together, with ventilation tunnels, over the top of a Double sided Board without air leakage between the layers.  Our biggest obstacle was to figure out how not to fill the vent tunnels with pre-preg during the lamination process.  After reviewing this Design, our staff came up with a process to laminate the two Boards together with a few uncommon processes.  Below you can view a cross section of the ventilation Tunnel through the layer structure, as well as the Board on Board view.

Vent Tunnel Cross Section:

Board on Board Bond:

If you like more information on this technology,  Please contact us at  PNC INC. 
You may also call us at 973-284-1600 and ask for Calvin Switzer, Q. A. Manager, PNC INC.

Circuit Design for Reliability

By Sam Sangani
PNC INC.
http://www.pnconline.com

 

As gate oxide thickness and dimensions of scale shrink in integrated circuit design, reliability problems occur and need to be considered early in the design process. Some of the more problematic issues include negative bias temperature instability (NBTI) and hot carrier injection (HCI). NBTI is a critical factor in PMOS devices and leads to current degradation, yield loss, and functional failure of integrated circuits. HCI has primarily affected NMOS devices, but today it is also a concern for PMOS devices. HCI is caused by hot carriers in the gate oxide that lead to oxide damages, which manifest themselves as current degradation, Vt shift, leakage current increase, etc.

Over time, both NBTI and HCI degrade device currents and will cause failures in integrated circuits. Circuit designers need to consider these reliability effects in the early stages of design to make sure there are enough margins for circuits to function correctly over their entire lifetime.

               

HCI and NBTI introduce a threshold voltage increase for the MOS. This may be a real issue for mixed signal applications. There is also a gm transconductance variation. This characteristic changes the gain of transistors, which may not be expected by analog designers.

With HCI and NBTI circuit simulation, designers can detect and locate potential issues. Because HCI is dependent of the horizontal electrical field in the channel, designers can improve the robustness of the devices by increasing their length. There is also an exponential decrease in hot carriers with a decrease in supply voltage. Designers can change the bias conditions of the devices where the issue is found.

NBTI problems are more difficult to fix. Designers can check voltage overshoot to avoid the damage caused by NBTI. They may decide to increase capacitive loads, increase the transconductances, or reduce the supply voltage of the function to reduce NBTI susceptibility.

Designers should make it a priority to study the IO blocks of their designs. Creating robust HCI/NBTI circuits is a new challenge for digital/analog designers.

Designers must need to know to design for reliability and they should be educated on additional reliability analyses. The value is the reduction of failure and redesign costs.

PNC Secures Ventec Polyimide Qualification

Friday, March 15, 2013 | PNC Inc.

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PNC Inc. is proud to announce its latest UL qualification of polyimide base materials. PNC has partnered with Ventec USA using VT-901 laminate and VT-901PP prepreg. These high-temperature, high-reliability products expand PNC’s wide product offering and introduces the manufacturer into new industries at a new competitive level. The qualification includes 0.002” inner layer cores and a minimum overall board thickness stack up of 0.025”. The qualification also includes a minimum outer layer copper thickness of half ounce copper while inner layer maximum is two ounce copper. 

 

PNC President Sam Sangani states,“We are proud to include the VT-901 in our product offering to our military and commercial customers. Ventec has proven to be a high quality partner in both material reliability and service in the U.S. that provides us the competitive edge we always look for.” 

 

Ventec recently achieved AS9100C certification and manufactures both in China and two locations in the U.S.

 

About PNC

PNC, an ISO 9001:2008, MIL55110, MIL31032, UL certified, and ITAR registered manufacturer has over 44 years of experience as a quality PCB manufacturer (est. 1968). Its northern New Jersey-based 38,000 square foot facility is a full service engineering and manufacturing site, offering both leaded and non-leaded finish solutions. They offer PCB design, PCB fabrication, PCB assembly, SMT stencils and membrane switches.

For more information,contact PNC Inc. via phone at (973) 284-1600, e-mail: info@pnconline.com, and www.pnconline.com.

Ventec USA is the US based distribution/QTA manufacturing wing of Ventec Laminates in Suzhou China. For more information, call (978) 521-9700

PNC Improvements - 2011

PNC Improvements - 2011
Process Improvements:
[1] Replaced old Tin Bath on Pattern plating line with a new and improved version for current latest PCB technology.
[2] Replaced old Tin stripper Bath with a new and improved version from Electrochemical. This new bath does not sludge out and
also, it is much better and improved version than what we previously had from PCI.
[3] New Water Circulation and Filtration system was installed on Film Strip line which removes most film particles so Nozzles does
not get clogged on Ringe water.
[4] Vibration System was installed on 5 tanks in plating line for better plating on Micro vias holes and for elimination of pitted
plating and mouse bites on surface/traces.
[5] New software was purchased for chemical analysis with SPC capabilities and various reporting capabilities.
[6] For better adhesion of Solder Mask on ENIG job, new process was installed after Aluminum Oxide and prior to Ringe/Dryer.
This process was tested and proven prior to final permanent installation.
[7] New Cu Bus Bar were purchased to replace all old one in plating Tanks. With total investment over $10,000
[8] New Racks are being tested now for ease of loading/unloading and for even plating purpose.
Building Improvements:
[1] Every single bathroom was completely re-done in production and office areas.
[2] Drilling Room was completely remodeled with New Ceiling, Lights, Colors, HVAC Ducts and Electrical work.
[3] Final Inspection Room was completely remodeled with New Ceiling, Lights, Colors, HVAC Ducts and Electrical work.
[4] Chemical Lab was completely remodeled with New Ceiling, Exhausts, Lights, Colors, HVAC Ducts and Electrical work.
New Hires:
Total 12 new employees were added in 2011, 3 of them with Master’s Degree in Chemical, Electrical and Electronics and MBA in
marketing fields.
New Equipment Purchased:
[1] New GIGA8888, 8 Spindle CNC Drilling Machine was Purchased
[2] Purchased Excellon MK VI Driller/Router
[3] Purchased new state of the art latest “Hollmuller etcher” from Germany
[4] Manufacturing Software upgrade to 64 bit system, D9 from Bacon Software, With Inventory control, purchasing, RMA, SCAR
built-in.
[5] Scoring Machine – March, 2011, Order was placed on 3/15/2011
[6] Post Etch Punch – March, 2011, Order was placed on 3/23/2011
[7] Laser for SMT stencil – April, 2011
[8] Resist stripper – Sept, 2011
[9] Part Washer – Nov, 2011
New Raw Materials:
PNC is currently testing High Tg 175, New VT-47 Laminates for Multi-layer and double sided PC Boards.
The following changes were made in last two months of 2011
[1] New and improved Etching chemistry starting 12/1/2011. This will hold higher Cu, better wall etching quality, better yield.
[2] New Inner Layer cleaning line that can handle 2 mil core
[3] New Tin Stripper Machine with improved chemistry from OMG
[4] Change HASL and LF‐ HASL Baths (Installation Date :12/23/11)
[5] Added New Etching controller
[6] Bough new Air knives set for Lead Free HASL for flat soldering (Installation Date:12/10/11)
[7] Ordered triple Roller Fluxer for fine line SMT PCBs(Installation Date: 12/28/11)
[8]Hired Process Engineer with 25+ yrs. of experience in various well known PCB shops in USA

RoHs Compliant PCBs from PNC Inc.

RoHs Compliant PCBs from PNC Inc.

RoHS Compliant

PNC Inc. is currently manufacturing RoHS compliant PCBs. We are currently using ISOLA (for multilayer and double-sided PCB’s) and NANYA (for double-sided PCB’s) brand products to manufacture our RoHS compliant PCBs. Although not limited to these brands, we are always looking for more product options to better serve you.

RoHS

We can provide you with UL approved PCB's boards with a variety of final finishes that meet the requirements of RoHS, REACH and Conflict Metals regulations

Since the adoption of the RoHS directive two additional regulations have been enacted that have had a significant effect on the PCB manufacturing industry; REACH by the EU and the Conflict Metals initiative in the USA. RoHS has matured through the last few years and the majority of the concerns voiced early on have not materialized. Similar legislative action has taken place in the Asian Pacific region including China and Japan among others. In the US, California has restricted the sale of electronic devices that do not meet the RoHS directive.

RoHS or the restriction of hazardous substances focuses on the use of six specific substances; Lead, Mercury, Cadmium, Hexavalent Chromium, Polybrominated biphenyls and Polybrominated diphenylether. The last two are fire retardants used in several types of plastic. The amount of each substance used in a product is limited to a maximum concentration based on the weight of homogeneous material used in a product.

Our High Tg materials (ISOLA 370HR and IS410) are specially formulated for superior performance though multiple thermal excursions, passing 6x solder tests at 288 degrees C. These materials are also optimized for enhanced drilling performance allowing high aspect ratio holes down to 8 mils. in diameter. Their unique resin chemistry provides CAF resistance with the benefit of long-term reliability of boards built with small feature designs. Along with these attributes, they bring improved productivity with their standard cure system while using current fabrication techniques.

PC Board Fabrication

PC board fabrication involves two aspects, namely:

* designing of circuit diagram
* inlaying it over the surface of the board

With the availability of high-tech machines, PC board fabrication has become simpler and economical.

Steps in PC Board Fabrication

Typically, PC board fabrication comprises the following steps:

Preparing artwork: This involves:

* preparing a basic circuit diagram on white paper.
* A conventional style is to use thin felt-tip pen, specially designed stencils or auto transferable stickers to prepare circuit diagram.
* Today’s contemporary style involves using CAD technology through specifically made software.
* CAD has simplified the designing process along with reduction in time.

Transporting design: At this stage, the artwork design is transferred onto the circuit board. A variety of techniques are used, such as:

* manual designing over the metal surface using a felt-tip pen.
* using self-adhesive films that are placed on the board’s surface.
* the use of photo-sensitive spray.
* employing special photo-sensitive circuit boards as such PC boards are expensive but have uniform photo sensitivity that facilitate high quality design transport.

Exposure to UV rays: The circuit board is then placed in a specially-designed box to get exposed to UV rays. A thin UV stream of 125W is used for this purpose. Following stages are:

* UV exposure transfers the circuit diagram onto the photo-sensitive plate.
* This stage requires specialist supervision to define the time of exposure.
* Later, the board is chemically treated with a mixture of caustic soda and water.
* It helps to remove the photographic film from the board and you get a printed circuit board with the circuit design inlaid.

Etching: The technique of plating copper on the surface of the circuit boards to form charge flow route is called as etching. Unwanted deposition of copper is chemically removed. The circuit board is then coated with a solder paste which brings forth a green color.

Drilling: This involves:

* making holes, called as vias, onto the circuit board.
* Vias allows for soldering of the electrical components.

World over, most of the large scale PC board fabrication is done through automated processes. US-based PNC Inc. excels in the manufacturing and repairing of PC boards. By producing double-sided and multiple circuit boards, PNC Inc has pursued excellence as its endeavor to meet client requirements.