Tips for PCBs and PCBAs Design

WHAT SHOULD I KNOW AND EXPECT? 

Successful CAD/CAM data transfer depends on data integrity and continuity. Data may originate from multiple sources and be stored in a variety of places throughout the process. Very strict conventions and data definitions are required. The pick and place CAD/CAM interface is relatively simple. It requires the designer to establish a useable coordinate system during the layout of the PCBA then merge the coordinates with the BOM and reference designators. Many of the popular layout tools have this feature built in. CAM uses automated equipment to handle and align the PCBAs. This automated equipment requires the use of alignment marks or “fiducials”. Some PCB fabricators will add the fiducials automatically, some will not. Therefore, it is always best for the designer to add the fiducial marks and export their coordinates along with the component coordinates. 

Data fields 

The following data fields must be exported in the following order into a single tab delimited file: 

1) Reference Designator (ie: “R1”, “R2”, “C1”, “U1”, etc) 

2) A unique part number. This is the VERGENT PRODUCTS part number for turnkey products. 

3) Description of the unique part number (ie: “RES, 10K 1% 1/10W 0603”) 

4) Board side for the given reference designator. This will be one of two values: 

“T” for component side or top. “B” for circuit side or bottom. 

5) X Coordinate in mills 

6) Y Coordinate in mills 

7) Orientation in degrees (ie: “0”, “90”, “180”, “270”) 

8) Polarity flag. This will be one of two values: 

“”Y” for components that are polarity sensitive. (ie: Diodes, LED’s, IC’s) 

“N” for components that do not matter. (ie: Resistors, certain capacitors) 

A sample file is given in Appendix A. 

PCBA Fiducials 

PCBA should be designed with at least two 50 mill round fiducials. 

The fiducials should be spaced as far apart as possible but within .250” from board edges. 

The solder mask must be clear over the top of the fiducial. Fiducials should be identified using the part number “FIDUCIAL” and a unique reference designator. 

Component labels 

To ensure data integrity the labels on all part containers must match the BOM exactly. Abbreviations shall not be used. 

Component presentation 

The presentation of a component (reel, tube, tray, other) is critical to automation. If a component is presented in a different manner then the machine program must be changed each time. Where possible standardize on a particular presentation and enforce it in your BOM.

Cut tape 

If components are inexpensive consider purchasing an entire reel as opposed to cut tape. While the cut tape may appear less expensive on the surface it can result in significant delays and costs overruns. Here is a real example for a 10K ohm 0603 resistor: 

Cut tape: 10 strips of 10 at $.70 each. Price: $ 7.00. 

Reel: 5000 parts. Price: $15.60. 

The reality is quite different because it takes time to handle and manage the cut tape: 

Cut tape cost: $ 7.00 parts + $17.00 handling + $104.00 feeder setup = $128.00 

Reel cost: $ 15.60 parts + $ 1.70 handling + $ 10.40 Feeder setup = $27.70 

Sometimes the component cost makes purchasing a reel prohibitive. In that case VERGENT PRODUCTS recommends purchasing a minimum of 100 pieces or the quantity required plus 20% in a contiguous strip. 

Silkscreen 

Reference designators should be places on the silk screen along with very clear polarity markings using IPC industry standards. 

“Do Not Load” (DNL) 

Components that have reference designators or a place to be loaded but will not be loaded must be clearly identified on the BOM. The nomenclature used in the industry is “DNL” for the part number. VERGENT PRODUCTS strongly recommends that all reference designators have part numbers assigned including the DNL. 

VERGENT PRODUCTS has assigned the part number 999-99-99999 as the dummy part number for DNL. 

What is the Current Board

First, what is the current board, printed circuit boards and electronic products have become indispensable for the vast majority of the major components. Single, double-sided PCB manufacturing is in the substrate material - copper clad laminate (Copper- (2lad I.aminates, CCI) on selectively drilling, copper plating, copper plating, etching, etc. processing, to obtain the desired circuit pattern. Another multilayer printed circuit board manufacturing, but also within the core of thin copper-clad laminates as substrate, the conductive pattern layers and prepreg (Pregpr'eg) alternately laminated by a one-time bonding together to form a conductive pattern layer interconnect between three or more layers. Thus it can be seen as a substrate material in PCB manufacturing, either CCL or prepreg in the printed board plays a very important role. It has a conductivity, insulation and support three aspects of the function. PCB performance, quality, manufacturing workability, manufacturing cost, the manufacturing level, etc., depends largely on the substrate material.

Second, the development history of the substrate substrate material and production technology, has gone through half a century of development, the world's annual output has reached 290 million square meters, the development time by electronic machine products, semiconductor manufacturing technology, electrical installation technology, printed circuit board technology innovative development driven from CCL 1943 phenolic resin substrate made into practical since the beginning of the development of the substrate material very quickly. In 1959, Texas Instruments Inc. to produce the first integrated circuit, for printing board of a higher high-density assembly requirements, thus contributing to the plywood production. In 1961, the United States Hazeltine Corpot ation company successfully developed a metal vias technology law multilayer technology. 1977 resin, BT resin to achieve a industrial production, to the world and provides a multilayer development of new low Tg substrate material. 1990 IBM Japan announced a photosensitive resin as the insulating layer laminated multilayer technology law, in 1997, including laminated plywood, including high density multilayer interconnect technology to develop maturity. At the same time, in order to BGA, CSP is a typical representative of the plastic package substrate has been rapid development. Late, some of the free bromine, antimony and other new green flame retardant board is rising rapidly in the 1990s, to the market. Of the substrate material already 40 years of development, it has formed the production scale of about 90 billion yuan in output value. In 2000, China's mainland CCL production has reached 64 million square meters, the output value of 5.5 billion yuan. In which the paper-based CCL production has ranked third in the world. But in technology, product varieties, particularly the development of new substrate, with foreign advanced countries there are still a considerable gap.

Third, the classification of the general PCB board substrate materials can be divided into two categories: rigid substrate material and the flexible substrate material. Important species is generally rigid substrate materials CCL. It is the reinforcing material (Reinforeing Material), impregnated with resin adhesive, by drying, cutting, folding synthesis blank, then covered with foil, with steel as a mold, in a high temperature and pressure in a hot press forming in the system into. Multilayer prepreg general use, it is CCL semi-finished products in the production process (mostly glass cloth impregnated with resin, dried processed). There are several classifications of copper clad board. Usually by reinforcing material plate is different, it can be divided into: paper-based, glass fiber cloth, composite matrix (CEM series), laminated plywood base and specialty materials group (ceramics, metal core group, etc.) five categories. If you press the resin adhesive plate used to classify different common paper-based CCI. They are: various types of phenolic resin (XPc, XxxPC, FR a 1, FR-2, etc.), epoxy resin (FE-3), a polyester resin. Common glass fiber cloth CCL epoxy (FR-4, FR-5), which is a glass fiber cloth type most widely used. There are also other particularity resin (glass fiber cloth, poly amide fibers, non-woven material is increased): modified bismaleimide triazine resin (BT), polyimide resin (PI) , diphenylene ether resin (PPO), maleic anhydride imide - styrene resin (MS), polycyanate ester resin, a polyolefin resin or the like. CCL by flame retardant classification can be divided into flame retardant (UL94 a VO, UL94 a V1 level) and non-flame retardant (UL94 HB level a) two boards. Nearly two years, with more emphasis on environmental issues, the flame-retardant CCL CCL in turn branch breed a new bromine-free material, it can be called "green flame retardant cCL". With the rapid development of electronic products and technology, to cCL higher performance requirements. Therefore, the performance of CCL classification, divided into general performance CCL, low dielectric constant CCL, high heat resistance, CCL (general board of L at above 150 ℃), low thermal expansion coefficient of the CCL (generally used on the package substrate ) and other types.

PCB market demand analysis

1, The rapid growth of production capacity in Asia, industry development trend of high quality manufacturers
Before 2000, 70% global PCB of value mainly is in Europe, America, Japan, Korea and other countries. Over the past decade, the rapid shift to Asia, so that PCB production capacity in Asia to grow rapidly. Asia, especially China has become the world's largest producer of electronic products, the downstream machine manufacturers need to make China the world's largest PCB production areas. 2008-2009 affected by the global economic crisis, there are many companies or because of the small production scale, low-tech, or the lack of market forecasts, but was forced to shut down. Since 2010, with the full recovery of the global electronic information industry, PCB overall demand growth, especially in the high-end product demand increased significantly, which is the domestic PCB manufacturer, especially the financial crisis experienced manufacturer of high quality test provides a broad space for development.
2, The downstream market demand for multi-wide, to accelerate the pace of industry transformation and upgrading
With the increasingly diverse needs of the downstream market, PCB products become even broader with the range of applications, including aerospace, military, automotive, home appliances, computers and mobile phones, and other fields, covering more and more areas, technical requirements are high, especially consumer electronic equipment and systems and entertainment applications development developed too fast, and showed a shorter life cycle characteristics, PCB is expected to pull off the favorable conditions in the new round of growth. Only to accelerate the pace of transformation and upgrading can we meet the growing needs of the market changes .

Solder mask

Solder mask or solder stop mask or solder resist is a thin lacquer-like layer of polymer that is usually applied to the copper traces of a printed circuit board (PCB) for protection against oxidation and to prevent solder bridges from forming between closely spaced solder pads. A solder bridge is an unintended electrical connection between two conductors by means of a small blob of solder. PCBs use solder masks to prevent this from happening. Solder mask is not always used for hand soldered assemblies, but is essential for mass-produced boards that are soldered automatically using reflow or solder bath techniques. Once applied, openings must be made in the solder mask wherever components are soldered, which is accomplished using photolithography.[1] Solder mask is traditionally green but is now available in many colors.
Solder mask comes in different media depending upon the demands of the application. The lowest-cost solder mask is epoxy liquid that is silkscreened through the pattern onto the PCB. Other types are the liquid photoimageable solder mask (LPSM) inks and dry film photoimageable solder mask (DFSM). LPSM can be silkscreened or sprayed on the PCB, exposed to the pattern and developed to provide openings in the pattern for parts to be soldered to the copper pads. DFSM is vacuum laminated on the PCB then exposed and developed. All three processes go through a thermal cure of some type after the pattern is defined.
In electronic design automation, the solder mask is treated as a layer of the printed circuit boards, and is described as a Gerber file like any other layer, such as the copper and silkscreen layers.

Electroless nickel immersion gold

Electroless nickel immersion gold (ENIG) is a type of surface plating used for printed circuit boards. It consists of an electroless nickel plating covered with a thin layer of immersion gold, which protects the nickel from oxidation.
ENIG has several advantages over more conventional (and cheaper) surface platings such as HASL (solder), including excellent surface planarity (particularly helpful for PCBs with large BGA packages), good oxidation resistance, and usability for untreated contact surfaces such as membrane switches and contact points.
Early ENIG processes suffered from reliability issues which caused the ENIG finish to separate from the copper pads, taking the parts with them. ENIG also does not wet as evenly or easily as HASL. In addition, a "black-pad" of nickel oxide would form during the immersion gold plating step, greatly reducing solder joint reliability. To remedy this, a layer of electroless palladium is plated onto the nickel to create ENEPIG surface finish.[1]
ENIG is a costlier finish, but offers the best characteristics for printed circuit boards. The process requires the most steps compared to other common finishing types.
The electroless nickel step is an auto-catalytic process that involves depositing nickel on the palladium-catalyzed copper surface. The reducing agent containing nickel ions must be replenished in order to provide proper concentration, temperature and pH levels necessary to create a consistent coating. During the immersion gold step, the gold adheres to the nickel plated areas through molecular exchange, which will protect the nickel until the soldering process. The gold thickness needs to meet certain tolerances to ensure that the nickel maintains its solderability.
IPC Standard IPC-4552 covers the quality and other aspects of ENIG finish on printed circuit boards.

Contact: Francis WEN
Email address: wonderful06@wonderfulpcb.com
Skype: wonderfulpcb-23