Components (BOM) Souring Service in Turnkey PCB Assembly


At MADPCB, Component Sourcing Service is provided both for active components and passive components. We understand the importance of reducing components cost and shortening PCB and PCBA manufacturing turnarounds by strategic components sourcing management. With long term working relationships with many component manufacturers and distributors both in domestics and overseas, we are able to purchase those hard to find parts at good prices and lead time, and offer them a very wide range of quality components. All part suppliers are audited by passing our quality standards and sourcing lead time requirement, and only trusted sources are permitted to procurement and application in your PCB assembly projects no matter in prototypes, low-volume and high-volume runs.

Partial electronic components types and brands we can provide listed as below,

Passive Components

Resistors, Capacitors, Magnetic (inductive) Devices, Memristor, Networks, Transducers, Sensors, Detectors, Antennas, Modules, …



Connector & Switch

MOLEX, TYCO, 3M, EPCOS, OMRON, Crydom, HIROSE, FCI, Weidmuller, PHOENIX, CONNTACT, ACES, FOXCONN, JST, SAMTEC, Amphenol, Cui Inc, C&K Components, E-Swtich, ...



Analog Device, ATMEL, AMD, Broadcom, Texas Instruments, Cypress, Epson, Everlight, Freescale, FDTI, Semtech, Intel, Infineon, Kingbright, Lite-On, Micron(Numonyx), MAXIM, Micrel, NXP, Osram, Renasas, Rochester, Samsung, Hynix, ISSI, SST, Spasion, STMicroelectronics, Vishay, Xilinx, Altera, Zarlink, Pulse, PLX Technology, Panjit, Marvel, Smsc, Rohm, Torex, Toshiba, ...


Passive Rectangular Components | SMD Package Type & Dimensions

Passive surface mount devices (SMDs) are mainly comprised of SMD resistors and SMD capacitors. There are several different standard sizes which has been reduced as technology has enabled smaller components to be manufactured and used. It will be seen that the devices size names are derived from their measurements in inches and millimeters.

Common Passive SMD Package Details

SMD Package Type


Imperial Code

Metric Code





0.25 x 0.125

6.3 x 3.2



0.20 x 0.10

5.0 x 2.5



0.18 x 0.125

4.6 x 3.0



0.125 x 0.10

3.2 x 2.5



0.12 x 0.06

3.0 x 1.5



0.08 x 0.05

2.0 x 1.3



0.06 x 0.03

1.5 x 0.8



0.04 x 0.02

1.0 x 0.5



0.02 x 0.01

0.6 x 0.3



0.016 x 0.008

0.4 x 0.2

If these sizes, the 1812, and 1206 sizes are now only used for specialized components or ones requiring larger levels of power to be dissipated. The 0603 and 0402 SMT sizes are the most widely used, although with miniaturing moving forwards, 0201 and smaller SMD resistors and capacitors are being used increasingly. When using SMD resistors, care must be taken to ensure that the power dissipation levels are not exceeded as the maximum figures are much less than for most leaded resistors.

Tantalum Capacitors SMD Packages

As a result of the different construction and requirements for tantalum SMT capacitors, there are some different packages that are used for them. These conform to EIA specifications.

Common SMD Tantalum Capacitor Package Details

SMD Package Type

Dimensions (mm)

EIA Standard

Size A

3.2 x 1.6 x 1.6

EIA 3216-18

Size B

3.5 x 2.8 x 1.9

EIA 3528-21

Size C

6.0 x 3.2 x 2.2

EIA 6032-28

Size D

7.3 x 4.3 x 2.4

EIA 7343-31

Size E

7.3 x 4.3 x 4.1

EIA 7343-43


Other Passive SMD Components

There are several types of other component that are not able to able to adopt the standard surface mount component sizes used by the majority of SMD resistors and capacitors.

Surface mount versions of components like many types of inductor, transformers, quartz crystal resonator, temperature-controlled crystal oscillators TCXOs, filters, ceramic resonators and the like may require different style packages, often larger than the ones that are sued for surface mount resistors and capacitors.

These packages are unlikely to adopt the standard surface mount component package sizes in view of the unique nature of the components. Whatever the package style chosen it must be able to fit the automated PCB assembly processes and be handled by a pick and place machine.


Transistor & Diode Packages

SMD transistors and diodes often share the same styles of package. While diodes only have two electrodes a package having three enables the orientation to be correctly selected. Although a variety of SMT transistor and diode packages are available, some of the most popular are given in the list below,

SOT-23 -Small Outline Transistor: The SOT23 SMT package is the most common outline for small signal surface mount transistors. The SOT23 has three terminals for a diode of transistor, but it can have more pins when it may be used for small integrated circuits such as an operational amplifier, etc. It measures 3mm x 1.75mm x 1.3mm.

SOT223 -Small Outline Transistor: The SOT223 package is used for higher power devices like higher power surface mount transistors or other surface mount devices. It is larger than the SOT-23 and it measures 6.7mm x 3.7mm x 1.8mm. There are generally four terminals, one of which is a large heat-transfer pad. This enables heat to be transferred to the printed circuit boards.


Integrated Circuit (IC) SMD Packages

There are many forms of package that are used for surface mount ICs. Although there is a large variety, each one has the areas where its use is particularly applicable.

SOIC -Small Outline Integrated Circuit: This surface mount IC package has a dual in line configuration and gull wing leads with a pin spacing of 1.27mm.

SOP -Small Outline Package: There are several versions of this SMD package:

  • TSOP -Thin Small Outline Package: This surface mount IC package is thinner than SOIC and has a smaller pin spacing of 0.5mm.

  • SSOP -Shrink Small Outline Package: This package has a pin spacing of 0.635mm.

  • TSSOP -Thin Shrink Small Outline Package

  • QSOP -Quarter-size Small Outline Package: It has a pin spacing of 0.635mm.

  • VSOP -Very Small Outline Package: This is smaller than the QSOP and has pin spacing of 0.4, 0.5 or 0.65mm.

QFP -Quad Flat Pack: The QFP is the generic type of flat package for surface mount ICs. There are several variants as detailed below.

  • LQFP -Low Profile Quad Flat Pack: This package has pins on all four sides. Pin spacing varies according to the IC, but the height is 1.4mm.

  • PQFP -Plastic Quad Flat Pack: A square plastic package with equal number of gull wind style pins on each side. Typically narrow spacing and often 44 or more pins. Normally used for VLSI circuits.

  • CQFP -Ceramic Quad Flat Pack: A ceramic version of the PQFP.

  • TQFP -Thin Quad Flat Pack: A thin version of the PQFP.

Component or Parts Overages Required During PCB Assembly

There is a potential for component or parts loss in a couple of different areas of the PCB assembly process. The first loss occurs when loading our automated SMT placement machines with components. The feeders (tooling that holds and advances the parts to the machine) require a certain amount of exposed tape during setup. This exposed part section is called the leader section on the SMT tape and is what allows the tape to start feeding into the feeder. Modern SMT placement machine feeder are very efficient in minimizing the amount of leader needed.

If the component is a part we have not used before, there is a component tranning phase, the SMT placement machine needs to go through to learn the new component. This generally requires only two everage parts. One part to train the machine and on to verify the training.

There is a chance of a mispick by the SMT placement machine during assembly. This mispick can cause the vision inspection system to reject the part. For larger parts, this is fine as the machine operator can remove the part from the reject bin on the machine, but for chip size resistors and capacitors, it is hard to identify, separete, and reload individual parts.

If a part was lost due to the above problems an exact number of parts was ordered, this would cause a manufacturing delay in the PCB assembly process. To reduce manufacturing delays, part overage is a necessary part of component sourcing process.

How Many Part Overages Need to Source?

At MADPCB, we want you to know exactly what and how many part overages are ordering. The Bill of Materials of your PCB assembly will display the additional quantity and price of part overage required for each individual line item. No labor charge is associated for additional parts for overage. You do not have to worry about part overages for turnkey sourced parts. MADPCB will calculate the overage required and order the parts for you. This reduces overall manufacturing delays by making sure all the parts arrive on time and there are no part shortage during assembly.

Component Size/Type

Need less than 20pcs

Need less than 50pcs

Need less than 100pcs


Order >=50pcs

Order >=100

Order >=150


Order >=50

Order >=100

Order >=150


Order >=100

Order >=150

Order >=200~250


Order >=100

Order >=150

Order >=200~250


Order >=100

Order >=150

Order >=200~250


Order >=150

Order >=200

Order >=250

IC, BGA, QFP, Connectors, Large size &Expensive Parts

Order 1-2 more

Order 3-5 more

Order 6-10 more


Continuous Strips & Tapes for Consignment or Partial Turnkey Assembly

  • Proper SMT machine setup and operation requires parts overages (or extra parts) because there is a small length between the feeder and the picking nozzle of the placement machine can’t be used. When it comes to pick and place process, the machine may throw away some parts, and the parts uploading to the feeders may be missed by manual. Unused and excessive parts supplier by you or purchased by us will be packaged and returned to you together with the PCB assemblies.

  • SMT parts which are not supplied on reels should be on one continuous strip of tape. If you need to assemble different PCB boards with the same SMT parts, please do not cut them into more strips, just keep them in the continuous strip of the tape or on the reels.

  • Standard of parts sourcing quantity or quantity provided for PCB assembly prototypes as the chart in Component Overages and Quantities. For high-volume PCB assembly runs, extra parts by percentage is ok for MADPCB. All extra parts are necessary for ensuring smooth assembling and shipping your assembled boards on time without shortage.

  • If some parts are provided by you, please ship each kit separately. Do not combine multiple orders in one box, unless kits are clearly marked and separated. All kits should have a packing list showing all the items and quantities included in the kit. We appreciate an email sent to us when tracking information, especially when drop shipping multiple components from your suppliers in Consignment or Partial Assembly project.