Designing a PCB with AutoTRAX DEX > Appendix

BCC - Bump Chip Carrier

BGA - Ball Grid Array

BGAs are perhaps one of the best performing SMT packages in use today, due to their high densities. The BGA is a descendent of the PGA, yet instead of pins, it has solder balls that can be placed directly onto the PCB. Because of their high density, BGAs are typically used to house microprocessors. Ball Grid Array BGA uses the underside of the package to place pads with balls of solder in grid pattern as connections to PCB.

The BGA is descended from the pin grid array (PGA), which is a package with one face covered (or partly covered) with pins in a grid pattern which, in operation, conduct electrical signals between the integrated circuit and the printed circuit board (PCB) on which it is placed. In a BGA the pins are replaced by pads on the bottom of the package, each initially with a tiny solder ball stuck to it. These solder spheres can be placed manually or by automated equipment, and are held in place with a tacky flux. The device is placed on a PCB with copper pads in a pattern that matches the solder balls. The assembly is then heated, either in a reflow oven or by an infrared heater, melting the balls. Surface tension causes the molten solder to hold the package in alignment with the circuit board, at the correct separation distance, while the solder cools and solidifies, forming soldered connections between the device and the PCB.

In more advanced technologies, solder balls may be used on both the PCB and the package. Also, in stacked multi-chip modules, solder balls are used to connect two packages.

Advantages

High density

The BGA is a solution to the problem of producing a miniature package for an integrated circuit with many hundreds of pins. Pin grid arrays and dual-in-line surface mount (SOIC) packages were being produced with more and more pins, and with decreasing spacing between the pins, but this was causing difficulties for the soldering process. As package pins got closer together, the danger of accidentally bridging adjacent pins with solder grew.

Heat conduction

A further advantage of BGA packages over packages with discrete leads (i.e. packages with legs) is the lower thermal resistance between the package and the PCB. This allows heat generated by the integrated circuit inside the package to flow more easily to the PCB, preventing the chip from overheating.

Low-inductance leads

The shorter an electrical conductor, the lower its unwanted inductance, a property which causes unwanted distortion of signals in high-speed electronic circuits. BGAs, with their very short distance between the package and the PCB, have low lead inductances, giving them superior electrical performance to pinned devices

Disadvantages

Noncompliant connections

A disadvantage of BGAs is that the solder balls cannot flex in the way that longer leads can, so they are not mechanically compliant. As with all surface mount devices, bending due to a difference in coefficient of thermal expansion between PCB substrate and BGA (thermal stress) or flexing and vibration (mechanical stress) can cause the solder joints to fracture.

Thermal expansion issues can be overcome by matching the mechanical and thermal characteristics of the PCB to those of the package. Typically, plastic BGA devices more closely match PCB thermal characteristics than ceramic devices.

The predominant use of RoHS compliant lead-free solder alloy assemblies has presented some further challenges to BGAs including "head in pillow" soldering phenomenon, "pad cratering" problems as well as their decreased reliability versus lead-based solder BGAs in extreme operating conditions such as high temperature, high thermal shock and high gravitational force environments, in part due to lower ductility of RoHS-compliant solders.

Mechanical stress issues can be overcome by bonding the devices to the board through a process called "underfilling", which injects an epoxy mixture under the device after it is soldered to the PCB, effectively gluing the BGA device to the PCB. There are several types of underfill materials in use with differing properties relative to workability and thermal transfer. An additional advantage of underfill is that it limits tin whisker growth.

Another solution to non-compliant connections is to put a "compliant layer" in the package that allows the balls to physically move in relation to the package. This technique has become standard for packaging DRAMs in BGA packages.

Other techniques for increasing the board-level reliability of packages include use of low-expansion PCBs for ceramic BGA (CBGA) packages, interposers between the package and PCB, and re-packaging a device.

Difficulty of inspection

Once the package is soldered into place, it is difficult to find soldering faults. X-ray machines, industrial CT scanning machines special microscopes, and endoscopes to look underneath the soldered package have been developed to overcome this problem. If a BGA is found to be badly soldered, it can be removed in a rework station, which is a jig fitted with infrared lamp (or hot air), a thermocouple and a vacuum device for lifting the package. The BGA can be replaced with a new one, or it can be refurbished (or reballed) and re-installed on the circuit board. Pre-configured solder balls matching the array pattern can be used to reball BGAs when only one or a few need to be reworked.

Due to the cost of visual X-ray BGA inspection, electrical testing is very often used instead. Very common is boundary scan testing using an IEEE 1149.1 JTAG port.

A cheaper and easier inspection method, albeit destructive, is becoming increasingly popular because it does not require special equipment. Commonly referred to as dye and pry, the process includes immersing the entire PCB or just the BGA attached module into a dye, and after drying, the module is pried off and the broken joins are inspected. If a solder location contains the dye, then it indicates that the connection was imperfect.

Difficulties during circuit development

During development it is not practical to solder BGAs into place, and sockets are used instead, but tend to be unreliable. There are two common types of socket: the more reliable type has spring pins that push up under the balls, although it does not allow using BGAs with the balls removed as the spring pins may be too short.

The less reliable type is a ZIF socket, with spring pinchers that grab the balls. This does not work well, especially if the balls are small.

Cost of equipment

Expensive equipment is required to reliably solder BGA packages; hand-soldering BGA packages is very difficult and unreliable, usable only for the smallest packages in the smallest quantities. However, as more ICs have become available only in leadless (e.g. quad-flat no-leads package) or BGA packages, various DIY reflow methods have been developed using inexpensive heat sources such as heat guns, and domestic toaster ovens and electric skillets.

BQFP - Bumpered Quad Flat Pack

CABGA/SSBGA - Chip Array/Small Scale Ball Grid Array

CBGA - Ceramic Ball Grid Array

CCGA - Ceramic Column Grid Array

CERPACK - Ceramic Package

CFP - Ceramic Flat Pack

CGA - Column Grid Array

CLCC - Ceramic Leadless Chip Carrier Packages

CLGA - Ceramic Land Grid Array

CQFP - Ceramic Quad Flat Pack,

CQGP - Ceramic Quad

CSBGA - Cavity Down BGA

CSOP - Ceramic Small Outline Package

CSP BGA - Chip Scale Package BGA

TBD - Ceramic Lead-Less Chip Carrier

DBS - DIL Bent SIL

DFN - Dual Flat Pack, No Lead

DLCC - Dual Lead-Less Chip Carrier (Ceramic) DLCC Graphic

DMP - Dual In-line Mini Molded Package

DQFN - Depopulated Quad Flat-pack; No-leads

EPTSSOP - Thin Shrink Small Outline Exposed Pad Plastic Packages

ETQFP - Extra Thin Quad Flat Package

FBGA - Fine-pitch Ball Grid Array

FCBGA - Flipchip BGA

FCPBGA - Flip Chip Plastic BGA

FFP - Flip-chip Fine Package

FleXBGA - Flexible Ball Grid Array

FLP - Flat Lead Package

fpBGA - Fine Pitch Ball Grid Array

HBCC - Heatsink Bottom Chip Carrier

HBGA - High Performance Ball Grid Array

HDIP - Heat-dissipating Dual In-line Package

HSBGA - Heat Slug Ball Grid Array

HSOP - Heatsink Small Outline Package

HTSSOP - Heatsink Thin Shrink Small Outline Package

HUQFN - Heatsink Ultra-thin Quad Flat-pack; No-leads

HVQFN - Heatsink Very-thin Quad Flat-pack; No-leads

HVSON - Heatsink Very-thin Small Outline; No-leads

HWQFN - Heatsink Very-Very-thin Quad Flat-pack; No-leads

HWSON - Heatsink Very-Very-thin Small Outline package; No leads

HXQFN - Heatsink eXtremely-thin Quad Flat-pack; No-leads

HXSON - Heatsink eXtremely Small Outline Package; No leads

JDIP - J-Leaded Dual In-Line J-Lead DIP Picture

JLCC - J-Leaded Chip Carrier (Ceramic) J-Lead Picture

LBGA - Low-Profile Ball Grid Array

LCC - Leaded Chip Carrier LCC Graphic

LCC - Leaded Chip Carrier Un-formed LCC Graphic

LCCC - Leaded Ceramic Chip Carrier

LCGA - Low-Profile Ball Grid Array

LFBGA - Low-Profile, Fine-Pitch Ball Grid Array

The Low-Profile Fine Pitch Ball Grid Array, or LFPBGA, is a smaller version of the ball grid array (BGA) package. It is basically an FBGA package that has a package height ranging from 1.2 mm and 1.7 mm. It is therefore thicker than the TFBGA and the VFBGA.

Typical LFBGA's have ball counts that range from 48 to 865 solder balls. The typical LFBGA ball pitch is 0.50 mm to 0.8 mm. A typical LFBGA is about 1.3 mm to 1.7 mm thick.

LGA - Land Grid Array LGA Graphic

LLCC - Leadless Chip Carrier

A leadless chip carrier (LCC or LLCC) is an integrated circuit package that has no pins/leads for contact. This surface-mount device makes use of metal pads at the outer edges to establish connection with the circuit board. Leadless chip carriers are popular, as they are light in weight, adaptable to a wide range of applications and are considered ideal for surface-mount applications.

A leadless chip carrier is usually square or rectangular in shape. Unlike other integrated circuit packaging, leadless chip carriers do not establish connection to devices by means of pins, but by means studs or metal pads provided around the periphery of the package. Due to reduction in weight, area and volume, leadless chip carriers are more durable and could withstand more vibration and shock compared to dual-in-line packages.

One of the salient features of a leadless chip carrier is its easy and convenient direct insertion to its socket mounted on the circuit board. It can also easily mount directly on the board. It is a low-cost solution for surface mounting, as it is lightweight and has no metallic external legs or leads. Unlike dual-inline packages, no holes are required for leadless chip carriers.

There are a few drawbacks associated with leadless chip carriers. The system is not considered homogeneous when leadless chip carriers are mounted to printed circuit boards. Failures of these systems have been common after limited stressing or thermal expansion. Most of these issues can be resolved by selecting the proper printed circuit board material.

LQFP - Low-profile Quad Flat pack

The Low Profile Quad Flat Pack, or LQFP, is a surface-mount IC package with leads extending from all four sides of the package body.

MCMBGA - Multi Chip Module Ball Grid Array

MCMCABGA - Multi Chip Module-Chip Array Ball Grid Array

MLCC - Micro Leadframe Chip Carrier

MLP - Micro Lead-frame Package MLP graphic

MQFP - Metric Quad Flat Pack (high pin count QFP)

MSOP - Mini Small Outline Plastic Packages

OBGA - Organic Ball Grid Array

ODFN - Optical Dual Flat No-Lead Plastic Package

PBGA - Plastic Ball Grid Array, PBGA graphic

PLCC - Plastic Leaded Chip Carrier

A plastic-leaded chip carrier (PLCC) has a rectangular plastic housing. It is a reduced cost evolution of the ceramic leadless chip carrier (CLCC).

A premolded PLCC was originally released in 1976, but did not see much market adoption. Texas Instruments later released a postmolded variant that was soon adopted by most major semiconductor companies. The JEDEC trade group started a task force in 1981 to categorize PLCCs, with the MO-047 standard released in 1984 for square packages and the MO-052 standard released in 1985 for rectangular packages. The PLCC utilizes a "J"-lead with pin spacings of 0.05" (1.27 mm). The metal strip forming the lead is wrapped around and under the edge of the package, resembling the letter J in cross-section. Lead counts range from 20 to 84. PLCC packages can be square or rectangular. Body widths range from 0.35" to 1.15". The PLCC “J” Lead configuration requires less board space versus equivalent gull leaded components, which have flat leads that extend out perpendicularly to the narrow edge of the package. The PLCC is preferred over DIP style chip carriers when lead counts exceed 40 pins due to the PLCC's more efficient use of board surface area.

POS Package on Substrate

PQFD Plastic Quad Flat --

PQFP Plastic Quad Flat Pack

PSOP Plastic Small-Outline Package PSOP graphic

QFN Quad Flat No-Lead

QFP Quad Flat pack QFP Graphics

QSOP Quarter Size Outline Package

SBGA Super BGA - above 500 Pin count

SDMP Shrink Dual In-line Mini Molded Package

SO Flat Pack - Small Outline Flat Pack IC

SOIC - Small Outline IC

SOJ - Small-Outline Package (J-Lead), SOJ

SOLIC - Small Outline Large Integrated Circuit (Gull-Wing Lead Wide Body)

SON - Small-Outline No-leads (leadless package)

SOP - Small Out-line Package

SSOP - Shrink Small-Outline Package

SOT - Small Outline Transistor Plastic Package

TBGA - Tape Ball Grid Array

TBGA - Thin Ball Grid Array

TDFN - Thin Dual Flat No-Lead Plastic Package

TEPBGA - Thermally Enhanced Plastic Ball Grid Array

TFBGA - Thin profile Fine-pitch Ball Grid Array

TQFN - Thin Quad Flat No-Lead Plastic Package

TQFP - Thin Quad Flat Pack TQFP Graphic

TSOP - Thin Small-Outline Package

TSSOP - Thin Shrink Small-Outline Package

TSOT - Thin Small Outline Transistor Plastic Package

TVSOP - Thin Very Small-Outline Package

TVSP - Thin Very Small Package

UFBGA - Ultra Fine-Line BGA

UTDFN - Ultra Thin Dual Flat No-Lead Plastic Package

VFBGA - Very thin Fine-pitch Ball Grid Array

VQFB - Very-thin Quad Flat Pack

VSO - Very Small Outline

VSSOP - Very thin Shrink Small Outline Package

VSP - Very Small Package

XQFN - eXtremely thin Quad Flat package; No leads

XSON - eXtremely thin Small Outline package; No leads