IPC CID

What do performance classes reflect?

Progressive increases in sophistication, functional performance, and frequency/intensity of inspection or stress testing

What are the three performance classes?

1-General Electronics 2-Dedicated Service 3-High reliability

Who is the end user?

The end user is the individual or agency that contracts the printed board or assembly to be designed and manufactured

Who determines the class of a product?

The end user

What would be in class 3 performance?

Military, medical, etc.

What is ambient temperature?

The surrounding environment that comes into contact with your product

What do producibility levels tell us?

Increasing complexity of tooling, materials, and processing. Yields increase as costs decrease, etc.

What increases with each producibility level?

Sophisitication

What is the zaxis aspect ratio?

Ratio between the nominal thickness of the board and the smallest drill size.

What is the most important special consideration in terms of electrical functionality that a designer must consult the EE?

Special keep out or keep in areas of the board.

Where should high frequency circuits be placed?

NEar the connector

Where should filtering caps be placed?

Near the source of power/gnd (at the connector)

What is least important to route in analog circuits?

Power and ground

What is a major consideration for component placement?

Will backwards compatibility be necessary?

What is Ohm's law?

V=IR

What is an important basic rule for a designer of a board?

Terminate unused logic pins with a pull-down or pull-up resistor.

What product safety testing regards flame retardants?

UL 94

How thick is half ounce copper?

0.7 mils (17 um thick)

What is the subtractive process?

Unwanted copper is etched away

What is the additive process?

Only wanted copper is added to the board

What must happen immediately after drilling the holes in the boards?

Hole deburring

What is an unsupported hole?

A hole in the printed board that does not contain plating or other conductive reinforcement

What is a supported hole?

A hole that has the inside surfaces plated or otherwise reinforced

What is a buried via?

A via that extends only between conductive layers with no exposure to the outside world

How do you measure annular ring on an external layer?

Including the plating the hole.

How do you measure annular ring on an internal layer?

Excluding the plating in the hole.

What are minimum annular ring requirements defined by?

Internal supported, external supported and external unsupported holes.

What is the most important factor in determining the minimum land size for a hole?

The max drill hole diameter

What are each of the following: a+2(b+c)+d

Min land size=max drill hole+2(min annular ring+etchback)+manufacturing

What is tolerance?

The amount of variation allowed in a dimension or location

What is breakout?

Drilled hole breaking out of the edge of the copper land

What is breakout acceptability?

Varies among class, where different amounts of breakout are allowed.

What is the MMC and LMC?

Can have dimensions given in a range, where MMC is most material condition and LMC is least material condition

What is the recommended electrical spacing from board edge?

16 mils PLUS the electrical requirement

What is it called when a land is only present to balance the construction of the board?

Nonfunctional lands

What is the clearance on nonfunctional lands?

0.25 mm (10 mils)

What is thermal relief?

Thermal relief is intended to remove sufficient copper to avoid heatsinking during the soldering processes while still meeting minimum current carrying requirements

How do you calculate thermal web size?

0.6(1/number of webs)landsize

What does CTE stand for and what are its units?

Coefficient of thermal expansion and ppm/C

What is the CTE for copper, brass and aluminum?

Copper: 17-18 ppm/C; brass: 19 ppm/C; aluminum: 24 ppm/C

What is special about thermal vias?

They must be connected to board-level planes

What does MTBF mean?

Mean time between failures; a higher mean time means your board is more reliable

What is the difference between burn-in testing and HAST?

HAST is usually destructive while burn-in is non-destructive and works to find infant mortality issues

What is a test coupon?

Companies find them beneficial and incorporate them into board production panels to not waste a good board in production

What is true of test probes?

They must make contact with every net, and can be ensured with the supplied net-list

What is the purpose of ICT, AOI, AXI?

To reduce board defect rates

What is the true purpose of ICT?

Locating manufacturing defects in the assembly process

What must be ensured before performing functional test?

Disable any free running oscillators

What can functional testing be considered?

A go/no go condition

What is required to perform in circuit testing?

Probe point locations and the netlist

When performing testing in a clamshell fixture, what is the minimum square land required?

36 mils (0.9mm)

Where can you guarantee no misses?

See IPC 7351-5.7 chart, answer is 1mm

What is an advantage of boundary scan technology?

Can perform virtual in-circuit testing

What board feature may also be used as a test point?

A wide exposed conductor may be used as a test point

What is the numbering convention of layers of a PCB?

Signal layers, solder mask, then legend layers

How are datum features used?

Position the printed board in relation to a set of three mutually perpendicular planes

What are the names of the datum planes?

Primary, secondary and tertiary

How are grids designed?

They are located with respect to a minimum of two datums

What is the international standard for grids?

0.5mm or increments of 0.05 mm grids

What does a grid system being basic mean?

The intersection of the lines has no tolerance

What are tooling holes?

Very tightly toleranced unsupported holes

What kind of tolerance is given to a tooling hole and why?

A -0" tolerance is specified so that the hole will never be too small to fit the pin

What is the common panel size in the US?

18" by 24"

Where can you place tooling holes on a densely populated design?

Can put the tooling holes on the borders of the panel

What are more useful board excision techniques for high volume production?

Punching (or blanking) dies to excise boards from fab panels is more efficient than other methods

How much does a Vscore cut from each side of the board?

1/3 of the thickness of the board

What helps illustrate electrical function by means of symbols?

The schematic drawing

What are examples of active components?

Transistors and diodes

What is important to know about a capacitor?

It can be polarized or unpolarized

What is important to know about a diode?

It has an anode (+) and a cathode (-)

What is the symbol for a photodiode?

The same as an LED, but with the arrows pointing in

What is the difference between an NPN and PNP transistor?

The emitter arrow points in towards the base for a PNP

When can you swap pins?

When your gates are within the same logic family

When can you swap gates?

When your gates are all within the same logic family and IC

What is done to the corners of the board tang on an edge connect board and why?

Chamfering, to prevent undue wear or damage of the board

What can be used as stiffeners if the electrical clearances are tight?

Fiber or plastic insulators can be located between the stiffeners and the conductors

What is the only component that you can place 2 leads in one PTH?

Bus bars

What are bus bars?

They are preformed components and serve the function of providing most of the power and ground distribution

What is a socket?

A receptacle used if a part frequently needs replacing

What must you consider when using a socket?

The pin numbers should be according to the device inserted into the socket

What are good candidates for sockets?

Components that have low CTE, such as leadless ceramic chip carriers

What is an insulated stranded wire?

Consists of multiple strands of wire that is purchased with a plastic coating

What is true of jumpers longer than 1"?

Adhesive must be applied for every 1" of the wire to the board

What is the primary purpose of eyelets?

Provide mechanical supports to the printed board and prevent mechanical damage to the substrate

What can component orientation help with?

Uniform orientation (all pin 1's in top left corner) reduces machine cycle time and can help drive down costs in production

What extreme cases do you need to consider for a hole and lead?

MMC- hole is at its smallest and lead is at its largest, LMC (opposite)

How do you calculate the hole diameter for a square component pin?

1.4*lead size+the appropriate material condition from the given table

Why is the heel fillet most important for gull wing components in soldering?

It provides the most stabilization and is a buffer against stress

What is the first consideration when deciding if a part can be transitioned from SMT to TH?

It must be determined if the leads can be bent or not

What is extra clearance around components required for?

The placement heads of the chip shooter

What side is exposed to wave solder with TH components?

The side opposite the component body

When is a clinched lead not acceptable?

When the pins are tempered and too stiff for bending

What should reference designators match?

The schematic or logic diagram

In a space limited design, what are the most important markings to include on your legend?

Polarity of polarized capacitors and diodes

What is the most significant risk if silkscreen gets onto solderable surfaces?

Reduced solderability to the component land

Who is responsible for the size and location of the legend features as part of the supplied artwork?

The designer

What must be established to eliminate skips and voids in lines and text in silkscreen?

a minimum line width

Where should reference designators be placed?

As close as possible to the device without being under it (just make sure it's visible)

What are typical sheet sizes for outputs from an ECAD program?

A or B size paper for ease of printing and PDF creation

What can a schematic be?

Hierarchical (partitioned into circuit functions into multiple levels of design details) or Flat (simple, stand-alone design)