FIELD OF INVENTION:
The present invention relates to the field of surface mount technology (SMT)
manufacturing process of PCBs in general, and in particular to a jig for the solder
paste printing of the SODIMM (Small Outline Dual Inline Memory Module) memory
sub-module. The jig results in substantial reduction in the set-up time for the PCBs
for solder paste printing.
BACKGROUND AND PRIOR ART:
The processor modules used in thermal power plant control equipments carries a
SODIMM (Small Outline Dual Inline Memory Module) memory sub - Module. This
SODIMM is a memory module designed to work as the storage device in the
Distributed Processing Module and contains 13 ICs in Micro - BGA (Ball Grid Array)
packaging distributed on either side of the 6 layered thin section (1mm) PCB. The
balls of the micro BGA are of the size 0.42 mm diameter and are placed at a pitch
of 0.8 mm. The PCB has ultra fine features which do not facilitate the
conventional In-Circuit -Testing methodology for ensuring auto detection of
assembly defects. In the absence of ICT, the module needs to be assembled
without any defects in accordance with International standards. Any defect arising
during manufacturing of these module will render the module unusable and rework
is not possible.

In view of the above, manufacture of these boards requires extremely high
precision in the SMT (Surface Mount Technology) manufacturing process. Owing to
the delicate design of the module and the size / spacing of the BGA balls, accurate
solder paste printing is a critical requirement for achieving the desired results.
In the prior art, the PCB is mounted on the frame of the solder paste printer with
pneumatic clamping. The PCB is supported from the bottom side using metallic
support pins and blocks. However precisely locating the pins and blocks for
supporting becomes difficult due to the presence of critical components on the
bottom side of the PCB. The unbalance created due to insufficient support at the
solder side leads to the PCB getting warped. The height of the solder paste cannot
be maintained uniformly. Apart from that the solder paste gets smudged during
the release of the PCB after printing due to the warpage created during the
printing process. All the above leads to insufficient solder during the soldering
process. Supporting the PCB from the solder side in an uniform way requires a
huge number of trials which is time consuming, many times up to 24 hours for
setting up. Moreover this process of trial and error is not repeatable and result in
considerable human fatigue. Every time the board is taken up for assembly, this
process is repeated leading to lower productivity apart from insufficient soldering
issues.

The present invention seeks to overcome the above mentioned drawbacks of the
prior art.
Indian Patent No.211649 dated 28* March 2008 (Heynen Ronald) discloses a
process and a device for aligning the substrate and a printing stencil in solder
paste printing. This document however is directed to proper alignment of the
substrate with respect to the stencil, achieved through optical sensing and related
alignment control.
US patent application 2009 0255426 dated 15th October 2009 (Doyle, Dennis G et
al) discloses a method and apparatus for placing substrate support components.
While this document is related to depositing viscous material which could be solder
paste, on an electronic substrate, the invention is directed to a substrate support
assembly, and particularly to a frame, a table and a plurality of support elements,
as well as a marking device coupled to the frame. An imaging system captures
images of the support surface of the table. A controller is used to verify whether
the marks on the support surface of the table are accurate.
None of the above documents however provides any hint of solving the problems
of the prior art described above.

OBJECTS OF THE INVENTION:
An object of the invention is to provide a jig which reduces the setup time
drastically, thereby increasing productivity.
Another object of the invention is to provide a jig that reduces human fatigue
considerably.
A further object is to allow for removal of the PCB without smudging of the solder
paste.
Yet another object is to eliminate warping of the PCB due to unbalance created by
insufficient support at the solder side leads during solder paste printing of the PCB.
A further object of the invention is to provide a jig which allows the solder paste
height to be maintained at a uniform level.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 is a photographic view of a bare SODIMM PCB placed on the base.

Fig. 2A shows the plan view of the jig according to the invention.
Fig. 2B shows the perspective view of the jig.
Fig. 3 shows details of a teflon support stem according to the invention.
Fig. 4 shows a photographic view of the separation of the PCBs after solder paste
printing.
The invention will now be described in detail in an exemplary embodiment as
depicted in the accompanying drawings. There can however be other
embodiments of the same invention, all of which are deemed covered by this
description.
DESCRIPTION
As stated earlier, in prior art, the setup time required to achieve a highly reliable
solder paste printing is very large. Due to long duration of set up the resultant
human fatigue is high with existing method of manufacture and results in poor
production performance. The jig according to the present invention eliminates the
above mentioned problems by making it easy for placement of the PCB, and for
solder paste printing on both sides of the PCB without any bowing due to the
squeegee pressure. After the completion of solder paste printing, component
placement and soldering, the two PCBs are separated out by breaking at the notch
provided as shown in figure-4.

The embodiments of the invention are described by the way of example with
respect to the accompanying photographs and drawings. The bare PCB placed on
the base is shown in figure-1. The assembly detail of jig is shown in figure-2. The
base (1) has a shallow recess (2) with a depth of 0.8 mm for accurate placement
of the 1 mm thick PCB, a middle support (3) to prevent the PCB from bending at
centre due to squeegee pressure while solder paste printing, and 20 precision
pointed support stems (4), as per figure 3 made of teflon material, are positioned
at multiple points to provide uniform support against pressure. Four locating pins
(5) are provided to ensure accurate positioning of the PCB in the deep groove (6)
at both ends of the base to facilitate easy lifting of PCB after the solder paste
printing without smudging of the solder paste. The jig is fixed on the solder paste
printer using pneumatic clamping on the sides. The PCB located on the jig is
placed in the solder paste printing machine for solder paste printing.
The solder paste printing method with the jig according to the invention is aimed
at reducing the setup time required for the printing with better reliability using
proper supporting and locating jig. The jig according to the invention has the
convenience of removal of PCB without smudging of the solder paste. The jig
developed provides a uniform support on the solder side of the PCB. This prevents
the PCB from getting warped. Accordingly the solder paste height can be

maintained at a uniform level and the solder paste does not get smudged during
PCB separation from the stencil. The jig supports 2 Nos. of PCB in a panel form
and hence the productivity is also enhanced. With the above jig the set up time
has been reduced to 2 hours as compared to 24 hours in prior art, and the
process has become fully repeatable resulting in lesser human fatigue.
The jig assembly is made of PRBCF material which is machined to provide a
shallow recess (2) for a depth of 0.8 mm. The recess suits the shape of the PCB
so that the PCB fits into it accurately. A middle support (3) is provided which acts
against the squeegee pressure and prevents warping or bending of the PCB during
the solder paste printing operation. This middle support forms an integral part of
the base.
A plurality of teflon support stems (4), typically 20 in number, are placed
strategically at 20 locations which are chosen very accurately. Utmost care is taken
in choosing the locations of the support stems so that no interference is
experienced with any component on the PCB. At the same time, support at the
bottom is uniform across the entire PCB surface.

The support stems (4) are made of Teflon. They prevent the PCB surface or the
component leads from damage during the printing process, which is caused by the
pressure developed on the supporting points. They are provided with sharp
conical shape so that the tip can be accommodated accurately in very critical
locations near the leads of the fine pitch ICs mounted on the PCB.
The jig has been provided with four locating pins (5) for accurate positioning of
the PCB on the base. This prevents the PCB from shifting from its location during
the printing process.
The jig has two deep grooves (6) at two ends of the PCB to facilitate easy lifting of
the PCB for removal after solder paste printing. This eliminates smudging of the
solder paste during removal of the PCB.
The jig has been provided with an accuracy tolerance, which matches with the
solder paste printing accuracy requirement of ±15 microns.

We claim:
1. A jig for SODIMM module solder paste printing made of PRBCF material
comprising of:
a shallow recess (2) having a depth of 0.8 mm and made to suit
the shape of the PCB;
middle support (3);
a plurality of Teflon support stems (4);
a plurality of locating pins (5); and
two deep grooves (6) at the two ends of the PCB,
characterized in that the middle support (3) prevents warping or
bending of the PCB during solder paste printing and in that the support
stems (4) are positioned in carefully chosen strategic locations to
prevent the PCB surface or the component leads from damage caused
by the pressure developed on the supporting points.
2. The jig as claimed in claim 1, wherein the number of the supporting stems
is 20.

3. The jig as claimed in claim 1, wherein the support stems (4) are provided
with sharp conical shape so that their tips can be accommodated in critical
locations near the leads of the ICs mounted on the PCB.
4. The jig as claimed in claims 1,2 and 3, wherein the supporting stems (4)
are positioned at 20 locations chosen carefully such that no interference is
experienced with any of the components on the PCB.
5. The jig as claimed in claim 1, wherein two deep grooves (6) are provided to
facilitate easy lifting of the PCB without solder paste smudging.
6. The jig as claimed in claim 1, wherein the setup time is 2 hours as
compared to the setup time of 24 hours in the prior art.
7. The jig as claimed in claim 1, wherein four locating pins (5) are provided for
accurate positioning of the PCB on the jig.

8. The jig as claimed in claim 1, wherein the jig has been provided with an
accuracy tolerance, which matches with the solder paste printing accuracy.

A jig for SODIMM module solder paste printing is made of PRBCF material. It
comprises of a shallow recess (2) having a depth of 0.8 mm and made to suit
the shape of the PCB; middle support (3); a plurality of Teflon support stems (4);
a plurality of locating pins (5); and two deep grooves (6) at the two ends of the
PCB. The middle support (3) prevents warping or bending of the PCB during solder
paste printing. The support stems (4) are positioned in carefully chosen strategic
locations to prevent the PCB surface or the component leads from damage caused
by the pressure developed on the supporting points.