PCB Circuit Board Testing, Inspection and Specification (2)

writer: G June 17, 2019

26. First Article:

For the purpose of smooth mass production, various parts or assembled products, whether the mature processes, equipment, materials and test inspections are still in the overall degree of coordination, and whether the products obtained can meet various established requirements. The requirements, etc., should be fully understood in advance so that there are opportunities for revision before mass production. The first or first small quantity of products that are trial-produced for these purposes are called First Article.

27. First Pass-Yield:

After manufacturing the finished product, after the initial inspection of each item to be inspected according to the established specifications, the proportion of the qualified products to the total number of products is called the first acceptance rate, or the process management is good or not. A specific pointer.

28. Fixture:

Refers to the tools that assist the product in various operations in the process, such as the dial for electrical measurement of the board, which is an important fixture.

29. Flashover:

Between the two conductor lines on the board surface (even if there is green paint), when there is a voltage, the surface of the insulator creates a "disruptive discharge" called "flashover".

30. Flatness:

It is a new expression of Bow Twist. In the early days of the wave soldering and inserting era, the requirements for the flatness of the board surface were not very particular. The upper limit of the IPC specification for the general board thickness was 1%. In the SMT era in recent years, the overall flatness of the board has a great influence on the solder paste solder joints. The degree of warpage of the unevenness must be less than 0.7% or even 0.5%. Therefore, in various norms, the term "flatness" with more intense concept is used instead of the words such as early plate bending and plate bending.

31. Foreign Material:

Generally speaking, there are some abnormal foreign materials in the pure or modulated raw materials, such as ash, sand, and resist crumb in the bath; or abnormal particles in the plate resin and plating. Narrowly refers to the foreign matter that is completely or partially concealed in the tin or solder layer to form a rough, tinned, or blocky appearance.

32. Gage, Gauge:

These two words refer to the measurement used for the measurement, such as the "hole gauge" of the aperture.

33. Golden Board:

Refers to the completion of the Continuity test (Testing), must have a well-prepared and correct material number board as a comparison, this standard board is called Golden Board.

34. Hi-Rel:

It is an abbreviation of High-Reliability. Generally, the board can be divided into three grades according to its required function and quality. The third grade (Class 3) is the highest level, which is "high reliability grade".

35. Hole breakout:

Referred to as "breaking" Breakout, it refers to the shaped hole drilled, some of which are located outside the copper plate area or the square copper pad area (Pad), so that the hole wall is not completely surrounded by the hole ring. That is, the hole ring has been broken and not complete, and the reliability of the interconnection of the interlayer interconnection is naturally greatly reduced. In general, the reason why the board is "broken out" is that the responsibility of image transfer skew is greater than the borehole.

36. Hole Counter:

It is a machine that uses the optical principle to automatically check the number of holes. It can quickly check whether the drilled board has leaking or plugging holes.

37. Hole void:

Refers to the wall of the through hole that has completed the chemical copper and the two electroplated copper. If the process is negligent or the condition of the bath is not good, the hole that sees "see the bottom" on the wall of the hole is called Void. Such holes in the hole wall have a bad influence on the quality of the socket welding, and are often collected in the hole due to the inhalation of moisture, causing gas to be ejected from the break at the time of high temperature welding, so that the through hole is The tin filling is blown into a cavity before solidification, so that the through hole becomes a blow hole (Blow Hole), so that the "hole" is actually the culprit of the blow hole.

38. Inclusion:

In the resin of the insulating sheet, there may be foreign impurities mixed in, such as plating or tin slag of the metal conductor, and various foreign materials such as non-conductors, etc., which are called Inclusion. Foreign matter in such a substrate may cause leakage or short circuit between the board lines or layers, which is one of the items for quality inspection.

39. Insulation Resistance:

It refers to the insulation resistance of the plate between the two conductors, and the volts is used as the expression unit. Here, "between two conductors" may mean two adjacent conductors on the board surface, or conductors between two adjacent layers of the multilayer board. The test method is to intentionally place the sample of the special fine comb line in a degraded environment with high temperature and high humidity to test the quality of the insulation. The standard test method can be found in the "Moisture and Insulation Resistance" test method of IPC-TM-650, 2.6.3D (Nov. 88). This term also has an approximate term SIR.

40. Isolation:

The correct meaning of this word refers to the spacing (Spacing) quality between the conductor lines of the board. The quality of this spacing must be checked by the electric method of the needle bed. According to the most widely used international standard IPC-RB-276, in its section 3. 12. 2. 2, in the process of DC test voltage 200V, after 5 seconds, the resulting resistance reading standard, Class 1 For low-end boards, it must be above 0.5MΩ; for Class 2 and 3 high-end boards, it must exceed 2MΩ. This kind of "isolation" is commonly known as "short" or "short". Leakage. Most manufacturers often refer to this electrical test as the "insulation quality" test, which is a common problem in China and foreign countries. Most of the industry has not been deeply aware of it. In fact, "Insulation" refers to the resistance of the board or the material itself. Sexual quality, not the quality of the system that expresses the "pitch" of the line. As for the copper slag, copper smash, or the lack of thorough cleaning of the conductive liquid, the "pitch quality" is bad. The industry’s long-term accumulation is ambiguous, and even the most basic definitions are blurred. There are two conventional electrical tests before the completion of the board shipment. In addition to the above Isolation, the other is to measure the continuity of the line. According to IPC-RB-276 3. 12. 2. 1., the connection quality of Class 1 low-order board must be lower than 50Ω at 5V test voltage. The quality of Class 2 and 3 high-order board powder must be less than 20Ω. This test is also known as the "open circuit". Therefore, the "Open Short Test" that everyone knows is able to catch up is actually a negative term for unprofessional. The correct statement of the profession should be "Continuity/Ioslation Testing".

41. Lifted Land:

The through hole of the circuit board is provided with a hole ring at both ends thereof, and is firmly attached to the upper as a shoelace buckle. When the board is subjected to intense heat during assembly welding, it will expand in the X, Y, and Z directions. Especially in the Z direction, since the expansion of the "resin portion" in the substrate is much larger than the "copper wall" of the through hole, the outer edge of the associated ring is also lifted up. Due to the adhesion between the matte side of the copper foil and the resin of the sheet, it has been damaged by the expansion and pulling. Therefore, when the board is cooled and contracted, the outer edge portion of the hole ring can no longer be retracted with the resin, so that the separation floats. The phenomenon. Such shortcomings were IPC-ML-950C (see 3.11.3) or IPC-SD-320B (see 3.11.3) before 1992, which stipulated that the maximum can only be 3 mil; and it is still required to remain attached but not floated. The open loop width must be at least half of the full loop width. However, this regulation has been completely cancelled in the newly issued IPC-RB-276 (Mar. 1992) (see Circuit Board Information Magazine, Issue 58 P.79, Table 10).

42. Major Defect:

Refers to the shortcomings found during the inspection, which is considered to be a serious shortcoming when the "confirmation standard" is seriously affected. If it is not recognized, it is called "minor defect" Minor Defect. Major is meant to express a major or important idea. If the main functions and main cadres are positive expressions, if they are used to describe negative "disadvantages", it seems that some are not suitable, so it is appropriate to translate them as "serious defects". The above criteria for identifying defects in PCBs are subject to various conditions, and those with explicit provisions are the most authoritative with MIL-P-55110D.

43. Mealing:

According to IPC-T-50E, the assembled circuit board is coated with a Conformal Coating, which may be dotted or flaked on the surface of the part. Part of the part floats, called bubble point or blistering.

44. Measling:

According to the explanation of IPC-T-50E, the fiber-optic cloth of the circuit board substrate has a local separation between the warp and weft yarns and the resin. The reason for this may be that the sheet is subjected to high temperatures and stress is pulled. However, once the FR-4 sheet is infiltrated by free fluorine chemicals (such as fluoroboric acid), the glass will be attacked more severely, and will have a regular white point on each interlace, called Measling.

45. Minimum Annular Ring:

When the Pads on the board are drilled and surrounded by the Annular Ring outside the hole, the width of the narrowest part will be the object of inspection, and the specification will accept the area. The lower limit value is called the "lower limit of the hole ring". This is an objective standard for PCB quality and technology. Since the preparation of the circular pad is first (ie, resisting and etching), and the drilling process is performed after the hole ring is present, the cooperation between the two process steps must be precise, and slight flashing may cause partial eccentricity, resulting in a ring ring. The range is wide and wide. The width data to be maintained at the narrowest point is specified in various written specifications, such as the various data in Table 6 of IPC-RB-276. In the case of a motherboard of a PC computer, it should be attributed to the Class 2 grade, and its "hole ring lower limit" must be 2 mil. According to the following two figures in IPC-D-275 (Figs 5-15 and 5-16), the inner ring ring will be defined without the hole wall, and the outer ring ring will have the hole wall. Calculated.

46. Misregistration:

In the circuit board industry, it refers to the front and back sides of the board, and some members (such as gold fingers or hole rings) that should be aligned with each other, when there is an offset, it is said to be "not right." This term refers especially to the eccentricity between the holes of the layers of the multi-layer board, which is called “inter-layer misalignment”. It is easy to measure the micro-slice technology. The accuracy of the data comes. The following picture is the explanation of "not sure" in the US military specification MIL-P-5511D. This word is called "coincidence" or "not coincident" in the mainland industry.

47. Nick:

The gap at the edge of the line on the board is called Nick. Another word, Notch, is often used mechanically and is less common on PCBs. Dish-down refers to the local depression of the line in terms of thickness.

48. Open Circuits:

After the thin layer inner layer of the multi-layer board is directly etched by the positive film method, the wire breakage often occurs, and it can be found by automatic optical inspection. If the wire is not broken, a small welding (Welding) wire-feeding machine can be used for remediation. . The outer break can be remedied by selecting the "Brush Plating" copper method (see photo). Under the strict requirements of modern requirements, such repair work must be approved by the customer in advance, and relevant documents must be kept in order to comply with the spirit of ISO-9002.

49. Optical Comparater:

It is a kind of physical or negative film board, through the transmission and reflection of light, and then through the lens magnification system or electronic focusing mode of the machine, the screen will get a clear picture to assist visual inspection. As shown in the OTP company's Optek 104 model, the image can be magnified up to 300 times, and the X, Y movable table surface driven by DC motor can flexibly select the fixed point to be observed. This kind of "optical contrast" has many functions and can be used for inspection, measurement, communication and discussion, etc., which are very convenient. In addition, a simple "learning comparator" is also installed on the program tape machine, so that the hole for the desired mark can be enlarged to make the correct paper with X and Y data.

50. Optical Inspection:

This is the development of mature inspection technology in the field of circuit boards in the past 10 years, also known as "automatic optical inspection" (AOI). It is the use of a computer to correctly store the line pattern in a digital way, and then perform a quick scan and comparison check on the produced board. This method can replace the visual inspection to find the abnormal situation of short circuit or open circuit, and it is most effective for the inner layer of the multi-layer board. However, this kind of "optical inspection" is not a panacea. It is inevitable that there is no way to catch it. It must also be combined with "electrical testing" to enhance the reliability of the shipping board.