FIELD OF INVENTION
This invention is related to assembly of printed circuit board .The invention is more particularly related to PCB assembly handling higher rating of current.
BACKGROUND
The Printed Circuit Board (PCB), also known as printed wire board are used in various electronic applications for interconnecting electronic components for predefined circuitry.
The components are interconnected through copper laminate/s which are etched on the PCB surface.
PCB is made up of Fire Retardant (FR) material, for example FR 4 (which is glass reinforced epoxy laminated sheets) or made up of using material laminates like aluminum.
PCB is can be single or multilayered with the layers connected through via’s (smaller diameter holes un plated in nature, used for interconnections of circuitry between layers of PCB) or plated through holes (PTH).Via’s can be buried (i.e. between internal layers) or through holes for multilayer PCB.
The PCB assemblies are used for various applications like Power converters (for ex. Regulators , AC to DC converters, DC to DC converters , Invertors , motor control applications, start – stop converters etc), Engine control units, ignition controllers, instrument clusters etc..
PRIOR ARTS AND PROBLEMS ASSOCIATED WITH PRIOR ARTS
When electronic assemblies mounted on PCB are required to operate at higher current applications, problems are faced with FR material to handle high currents

using copper thicknesses with 105 microns which is generally used thickness available in the industry. In case copper thickness is increased beyond 105 microns, it leads to reduction in yield i.e. leads to more rejection.
When high currents like more than 15 amps are handled, copper thickness needs to be higher and maximum thickness used with FR material can handle currents in the order of 20 amps. i.e. with regular FR material, currents more than 20 A is difficult to handle only with the copper attached to it.
For currents higher than 20 amps, FR materials with 105 microns of copper thickness cannot be used for inter connections of electronic components due to its incapability of handling high temperatures.
In past, for handling currents more than 20 amps, there are PCB assemblies where heat sink is used to place power components or usage of aluminum laminates to handle higher currents. In these designs, bigger power connectors are needed which consume space as well as increase in cost.
For handling currents more than 20 amps, designs are used with two separate PCB , one with FR material which interconnects control circuitry ( for ex. Analogue/digital circuitries with or without micro controllers) and power components ( for ex MOSFETS, SCRs, IGBT, high power transistors) are placed or mounted on aluminum laminates which are normally connected to heat sinks or casing acting as heat sink. These types of PCB assembly needs wave soldering process for all the through hole electronic components, which gives lower manufacturing quality as compared reflow/robotic/selective soldering process and consumes more manufacturing time.
However, the problem associated with high current applications prior arts that FR material and aluminum laminates needs to be separated from each other to avoid thermal breakdowns of the components or the electronic circuitry and their functionalities.

This further needs costlier PCB mounted connectors to feed the power in and take the power out from PCB assembly.
Additionally, for interconnecting the FR material PCB and aluminum PCB, flexible wires are used .This leads complexicity in manufacturing and the layout of the overall assembly. Also, the power components which are assembled on aluminum PCB are directly connected to the FR material PCB where manufacturability is issue in terms of alignment of PTH on FR material to the lead/terminals of the power components.
Other ways of connecting FR PCB material and aluminum PCB is through connecting power terminals. In this type of design, FR material PCB is directly placed above the power components on the aluminum PCB, leading to no gap between FR material PCB and power component. This leads transfer of heat from power components to control circuitry mounted on FR material PCB. Both PCBs are connected to the terminal strip on the power connector using a semi circular PTH (plated through hole) placed on the FR material PCB. This design is subjected to high temperature stress on the PTH of the FR material PCB .Assembly of two PCBs needs to be done by manual soldering which leads to poor quality of manufacturing. Further, in such designs, no electronic components can be placed above the power components and PCB tracks can’t be routed as they subjected to high thermal stress. Moreover, PCB tracks routing to be spaced away from power components, thus leading to bigger size of PCB.
Another alternative is to completely isolate power circuitry and control circuitry in two different PCB assemblies and they are placed apart which are interconnected through wiring harness. This requires more space and separate housings and mounting brackets for packaging.

OBJECTIVES
Applicant has tried to mitigate all the problems associated with above mentioned prior arts and provide an improved PCB assembly for handling higher order of currents.
Accordingly, one of the objectives of the invention is to isolate two PCBs with a predefined space to avoid direct thermal transfer between each other and between components mounted over the PCBs.
Yet another objective to prevent usage of PCB mounted power connectors.
Yet another objective to have ease of manufacturing.
Yet another is to reduce size of PCBs and use of a common housing for PCB assemblies.
Yet another objective is to reduce the packaging space and cost of assembly.
Yet another objective is to allow mounting of components at the bottom side of one of the PCB, thus reducing size of PCB.
Yet another object of the invention is to increase life and reliability of electronic comments and assembly.
Yet another objective is to deploy better soldering processes like reflow/robotic/selective soldering process.
SUMMARY OF INVENTION
An improved PCB assembly comprising atleast two PCBs mounted with electronic & electrical components, power input and output connections, wherein; the PCBs are

of different material and are spaced apart and connected to each other by connecting means thermally isolating components mounted on each PCB; power input and output connections are through wiring harness and provided to the PCB without using any PCB mounted connector.
Preferably high current handling electronic and electrical components are mounted over one of the PCBs and low current handling electric and electronic components are mounted over other PCB.
Preferably the material of PCB mounted with high current carrying components is made up of aluminum base material and the material of PCB mounted with low current carrying components is made up of FR base.
Alternatively, some of the high current carrying component and low current carrying components can be mounted on each PCB.
Preferably the PCBs are interconnected for low power signals by atleast one connecting means i.e. board to board connectors
Preferably connecting means are mounted header or board stackers.
Preferably the said mounted headers have atleast two pins.
Preferably the mounted header is connected to PCBs using reflow soldering process and robotic soldering process.
Preferably power input and output connections are through wiring harness connected directly to PCB without any connector.
Preferably the power input and output connections are connected to the PCB having aluminum base.

The board to board connectors (for ex. mounted headers, board stackers PCB board mounted plug Surface mounted PCB headers plug or socket type connector) and comprise stopper, height adjuster arrangement, support arrangement, soldering terminals as appropriate for the application.
The invention is described in detail along with accompanying drawings
DETAIL DESCRIPTION OF DRAWING
Figure 1 and 2 illustrate PCB assembly according to one of the prior art.
Figure 3 illustrate PCB assembly according to another prior art.
Figure 4 illustrate PCB assembly according to another prior art
Figure 5 illustrates PCB assembly according to one of the preferred embodiments of
invention.
Figure 6 illustrates exploded view of PCB assembly of figure 5 along with heat sink.
Figure 7 illustrates assembled view of PCB with heat sink.
Figure 8 is detailed view of connecting means.
Figure 9 illustrates socket / plug type board to board connector.

PART NUMBER PART NAME
1. FR PCB Control Circuit
2. AL PCB Power Circuit
3. PCB Mounted Connector
4. Power Components
5. Heat Sink Or Casing
6. Metallic Strip Terminal
7. Soldered to semi circular PTH
8. Wires are soldered between two PCBs for signal/power connections
9. Power circuit assembly
10. Control circuit assembly

11. Wiring harness interconnect
50. Improved PCB assembly
51. AL PCB Power Circuit of present invention
52. FR PCB Control Circuit of present invention
53. Header connectors or board stackers
53a. Two Pin Header
54. Wiring harness assembly of present invention
55. Wiring harness in present invention
56. Aluminum Heat Sink
57. Stopper and height adjuster
58. Support and soldering terminal
In the prior art according to figure 1 and 2, FR material based PCB (1) is placed above the aluminum material based PCB power circuit assembly (2). PCB mounted connector (3) is soldered to the Aluminum PCB assembly (2). Power components (4) are soldered to the Aluminum PCB (2). The FR PCB (1) when assembled, it rests on the power components (4) without any gap. On operation of this electronic assembly, high currents are handled by the power components which create high temperatures. High temperatures are directly transferred to the FR PCB (1), Due to this problem no electronic components can be mounted at the bottom side of FR PCB (1). Also, PCB tracks cannot be routed above the power components of aluminum PCB and on the bottom side of FR based PCB.
Moreover thermal stress on the components placed in the FR PCB (1) reduces the life and reliability of the electronic assembly.
In the above prior art, Figure 2 explains the usage of high current handling PCB mounted power connector (4). FR material based PCB (1) is soldered to the connector using semi-circular PTH (7). Soldering is done manually, where solder balls are possible to enter the assembly creating trouble during manufacturing. Moreover since high current is passed through the metallic strip terminal (6), the PTH (7) will be exposed to high temperature stress, leading to breakage of electrical

connection and malfunctioning or loss of functionality of the electronic assembly. Further the power connectors are costly items.
The Aluminum material based PCB (2) is mounted on the casing which acts as heat sink. The complete assembly is preferably potted using epoxy material or covered using plastic or metallic casing without usage of epoxy material. Epoxy material is preferably a proportional mixture of resin and hardener which is filled inside the electronic assembly and its vaccumised. Later they are cured using oven or through natural process.
Figure 3 shows another prior art wherein interconnections between the two PCB’s (1, 2) are done through bare wires (8) or insulated wires which are soldered to both the PCB’s. in this prior art ,routing of the wires in the PCB assembly is complex and are prone to damage if not routed away from the thermally hot power components . As the wires are flexible in nature, desired fixed amount of gap or space between two PCBs cannot be achieved. Here additional length of wires is required for manufacturing and cause packaging problem of the wire. Further the wires are to be soldered manually which consumes time and may lead poor quality.
Figure 4 illustrates other prior art where High current power circuitry (9) and lower current control circuitry (10) is placed far apart with two different housing and they are connected to each other by wiring harness (11). This type of designs requires additional cost for separate housing and additional packaging mounts on the application.
According to figures 5 to 8, the improved assembly (50) comprises two PCBs (51, 52) spaced apart and connected with a mounted header or board stackers (53). Various electronic components are mounted over these PCBs.
One of the PCB (51) is of aluminum base material and other PCB (52) is of FR base material. The PCB can be single layered or multiple layered.

The PCB (51) is mounted with power components (for ex MOSFETS, SCRs, IGBT, high power transistors) and PCB (52) is mounted with control circuitry control components (for ex. Analogue/digital circuitries with or without micro controllers).
The mounted header is first connected to PCB (51) by reflow soldering process and then connected to PCB (52) by robotic/selective soldering process. Any suitable connection process or soldering process can be employed .However, wave soldering process can be avoided which has comparatively poor quality and is time consuming process.
The connection of PCBs through mounted headers allows creating a desired space or gap between two PCBs. Thus preventing direct heat dissipation by power components of to control circuitry components mounted on FR based PCB. Thus improving life and reliability of these components and their functionalities.
Thus, this does not restricts the placement location of control circuitry components and routing arrangements/PCB tracks on the FR based PCB. Also electric or electrical components can be mounted on bottom side of FR PCB, thus requiring comparatively reduced size of PCB when compared with prior arts.
More than one mounted headers can be employed for connecting PCBs .The mounted header can have two pins (53a) or more.
The board to board connectors (for ex. mounted headers, board stackers PCB board mounted plug Surface mounted PCB headers plug or socket type connector) and comprise stopper, height adjuster arrangement, support arrangement, soldering terminals as appropriate for the application.
For example ,the board to board connectors (for ex. mounted headers, board stackers) comprise stopper and height adjustment arrangement(57) at its one end and support and soldering terminal arrangement (58) at opposite end.

The power input and output connection (54) is provided to PCB (51).The power input and output connections are through wiring harness (55) connected directly to PCB, may be through soldering process. This prevents use of any PCB mounted with high power connector/s.
Use of wiring harness for power input and output connections saves approximately 80% cost as compared to power connectors.
The PCB assembly is fastened to a aluminum heat sink (56) and filled up with Epoxy material to avoid damage to PCB assembly from any outside components/environment.
As per one of the embodiment, the printed circuit board assembly shall comprise of a first PCB [51] with components mounted over it and a second with components mounted over it. A board to board connector means shall be disposed therein between the component mounting surface area of the PCB [51] and PCB [52], the said board to board connector reflow soldered at PCB[51] end, and which robotically / selectively soldered at PCB [52] end. And also the said PCBs [51, 52 ] are connected to power input and output connections without using any PCB mounted connector.
In another embodiment, the first PCB (51) may be aluminum based and the second PCB (52) may be fire retardant base material. The first PCB (51) is mounted with high power components and second PCB (52) mounted with low power components.
Furthermore the board to board connector means may be a single board to board connector. Alternatively there can be more than one board to board connector disposed therein between the said first PCB [51] and said second PCB [52].
The said board to board connector means may be selected from a range of known connector means such as a mounted header type, a stacker type, a socket type or plug type and comprising single pin or plurality of pins [53A]

Furthermore the PCB assembly may be fastened onto an aluminium heat sink [56] and filled up with epoxy material.
The other embodiment displays a unique wiring arrangement i.e., a soldered wiring harness [55] connecting the power input and output connector to the said PCBs.
The power input may be connected to one of the PCB, power output connected to other PCB or power input and power output may be connected to first PCB or alternatively to the second PCB.
The invention also discloses a method of arranging components on a printed circuit board assembly. The arrangement comprising the steps of arranging power components on a first PCB [51] and arranging control circuit components on a second PCB [52]. Disposing a board to board connector means between the PCB [51] and PCB [52]. The method involves connecting the board to board connector means firstly to PCB [51] by reflow soldering process and connecting the board to board connector means thereafter to PCB [52] by robotic / selective soldering or any conventional soldering process but excepting wave soldering process. The power input and output is connected to PCBs with soldering wiring harness [55] without using any PCB mounted connector.
Typically aluminium based PCB may be selected as the first PCB and fire retardant based material PCB as the second PCB.
The method also includes a step of mounting high power components on the first PCB and mounting low power components on the second PCB and arranging a single connector or multiple connectors between the PCBs.
The connector may be selected from a range such as mounted header type, a stacker type, a socket type or plug type connector means each having single or plurality of pins [53A].

The method may involve additionally a step of fastening the PCB assembly on to an aluminium heat sink and filling up with epoxy material.
The method does involve soldering wiring harness [55] for connecting power input and output connector to the PCB without using any PCB mounted connector.
Finally the method may also include the step of connecting the power input to one of the PCB and power output connected to the other PCB.
Thus the above described improved PCB assembly has ease of manufacturing, can handle higher order of current without damaging other components and is cost effective. This assembly can be packaged in less space where space constraints are predominant such as in automotive application.
Variations and alternation in present invention known to person skilled in the art deemed to be covered under scope of invention.

WE CLAIM:
1. A printed circuit board assembly comprising of :
a. a first PCB [51] with components mounted over it,
b. a second with components mounted over it, and
c. wherein board to board connector means disposed therein between the
component mounting surface area of the PCB [51] and PCB [52], the said
board to board connector reflow soldered at PCB[51] end, and which
robotically / selectively soldered at PCB [52] end,
and wherein the said PCBs [51, 52] are connected to power input and output connections without using any PCB mounted connector.
2. The printed circuit board assembly as claimed in claim 1 where in first PCB (51) is aluminum based and second PCB (52) is of fire retardant base material.
3. The printed circuit board assembly as claimed claim 2 wherein the first PCB (51) is mounted with high power components and second PCB (52) mounted with low power components.
4. The PCB assembly as claimed in claims 1 wherein the board to board connector means may be a single board to board connector or plurality of board to board connector disposed therein between the said first PCB [51] and said second PCB [52].
5. The PCB assembly as claimed in claim 1 wherein the said board to board connector means may be a mounted header type, a stacker type, a socket type or plug type and comprising single pin or plurality of pins [53A].
6. The PCB assembly as claimed in claim 1 wherein the PCB assembly is further fastened onto an aluminium heat sink [56] and filled up with epoxy material.

7. The PCB assembly as claimed in 1 wherein a soldered wiring harness [55] connects the power input and output connector to the said PCBs.
8. The PCB assembly as claimed in claim 7 wherein power input is connected to one of the PCB and power output connected to other PCB.
9. The PCB assembly as claimed in claim 7 wherein the power input and output are connected to the first PCB.
10. The PCB assembly as claimed in claim 7 wherein the power input and output are connected to the second PCB.
11. A method of arranging components on printed circuit board assembly, the arrangement comprising the steps of :
a. arranging power components on a first PCB [51],
b. arranging control circuit components on a second PCB [52],
c. arranging a board to board connector means between the PCB [51] and PCB
[52],
d. connecting the board to board connector means firstly to PCB [51] by reflow
soldering process,
e. connecting the board to board connector means thereafter to PCB [52] by
robotic / selective soldering or any conventional soldering process but
excepting wave soldering process, and
f. Connecting power input and output to PCBs with soldering wiring harness
[55] without using any PCB mounted connector.
12. The method as claimed in claim 11 further comprising selecting aluminium
based PCB as the first PCB and fire retardant based material PCB as the
second PCB.

13. The method as claimed in claim 11 further comprising the steps of mounting high power components on the first PCB and mounting low power components on the second PCB.
14. The method as claimed in claim 11 further comprising the step of arranging a single board to board connector or arranging a plurality of board to board connectors between the first PCB and the second PCB.
15. The PCB assembly as claimed in claim 11 further includes selecting mounted header type, a stacker type, a socket type or plug type connector means each having single or plurality of pins [53A].
16. The PCB assembly as claimed in claim 11 further includes a step of fastening the PCB assembly on to an aluminium heat sink and filling up with epoxy material.
17. The PCB assembly as claimed in claim 11 further including soldering wiring harness [55] for connecting power input and output connector to the PCB without using any PCB mounted connector.
18. The PCB assembly as claimed in claim 17 further including the step of connecting the power input to one of the PCB and power output connected to the other PCB.