Pin-in-Paste Hole Fill
Autor: Marcelo Chirai | Publicado: 2017-01-19T21:02:00-02:00



July 7, 2016 



Pin-in-Paste Hole Fill 



We are about to implement Pin-in-Paste technology.



How can we ensure proper plated hole fill during the screen printing 
process? Will the process require using a different solder paste than 
the one we use for pure SMT assemblies?




R. L. 





Experts Comments



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Paste-in-hole
 processes are somewhat more complex than traditional SMT from a process
 control standpoint, but with good engineering practices and the 
properly optimized stencil, it can be a
very controllable process for many users. 

The key is doing some math on the front end and determining how 
much paste will be needed to fill the space between the barrel of the 
through-hole and the lead of the component. 

Since paste is generally about 50-55% metal by volume, you will 
generally find that you need to overprint the pad area to ultimately 
deliver enough solder to the solder joint. Various stencil design 
techniques will work; contact your solder paste and/or
stencil supplier for more detailed pointers.



As for picking the right paste for paste-in-hole applications, many 
standard solder pastes may drop into this type of process without any 
issues. However, there are two additional solder paste performance 
requirements for paste selection in paste-in-hole versus
traditional SMT. 

These include coalescence behavior and anti-dripping behavior. The 
coalescence behavior becomes more of an issue than usual due to the 
likelihood of overprinting onto the solder mask on the top side of the 
board. The anti-dripping requirements stem from
the fact that some pastes can drip off the bottom of the component lead 
upon heating, resulting in less solder than expected for the solder 
joint. 

This can be avoided by selecting a solder paste that was designed not to drip in a paste-in-hole application.







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Brian Smith

General Manager - Electronic Assembly Americas

DEK International

Mr. Smith has 
been supporting customers in the electronics assembly industry since 
1994. His expertise is focused on solder paste printing and reducing 
soldering defects. He holds a BS in Chemical Engineering
and an MBA in Marketing. He has authored several papers in trade 
magazines and at industry conferences. He is an SMTA Certified Process Engineer. 


To 
ensure proper plated hole fill during the screen printing process you 
must have the proper volume of solder paste. Here's an example of the 
formula you can use:

H=Hole diameter

D=Lead diameter

T=Board thickness

L=Width of lead in the X direction (For square lead)

W=Width of lead in the Y direction (For square lead)

Pi =3.14

Hole Volume (HV)=(3.14)(H/2)(H/2)(T)

Lead Volume (LV)=(3.14)(D/2)(D/2)(T) (For round leads)

Lead Volume (LV)=(L)(W)(T) (For square or rectangular leads)

Annular Ring Area(RA)=(3.14)(L/2)(L/2)-(3.14)(H/2)(H/2)

Solder volume (SV)=HV-LV

Print Volume (PV)=(2)(SV) (50%) 

Print Area (PA)=(F)(PV)/stencil thickness

F=Inspection Factor

.7=no fillet

.9=fillet on both sider

0.8=fillet on primary side

1.0=large fillet on both sides








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Joe Karcewski

Product Manager

APS-Novastar, LLC

Joe Karcewski 
has been a Process Engineer for 16 years in the industry. He is a 
certified IPC-A-610 trainer and is presently working at APS-Novastar as a
 Product Manager for Soldering Systems including
Selective Soldering systems. 


The best solution for the Pin-in-Paste process is the ProFlowR enclosed head system.

The main reason for this is that ProFlow allows independent control
 of paste pressure and, therefore, the ability to control the amount of 
paste fill for the through-hole apertures. 

If you are unable to use ProFlow, then a 45 degree squeegee can 
increase the paste pressure. But, if the board is thicker than 1mm, 
several print stokes will be required, which could degrade the SMT 
deposits.

Standard solder paste should be used for this application.








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Clive Ashmore

Global Process Manager

Dek Printing Machine

Mr. Ashmore is
 responsible for the Global Applied Process Engineering group for DEK. 
Clive specializes in all aspects of manufacturing engineering, with 
special emphasis on mass imaging technologies.



Same 
paste should work. You can calculate amount of paste required knowing 4 
items: pin dimension, board thickness, hole size, and annular ring size.
 Paste to solder shrinkage is usually about
50%. 

Paste volume can be achieved in 3 ways: Overprint, Step-up Stencil, through-hole paste fill.

Good reference paper is in SMT Magazine Nov and Dec 2006 "Intrusive Reflow for Lead Free paste."








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Bill Coleman

Vice President Technology

Photo Stencil

For over 18 
years, Dr. Coleman has been the vice president of technology for Photo 
Stencil, working closely with customers to understand their printing 
requirements. His
efforts have resulted in several new stencil products. 


The 
use of an off-line x-ray inspection system post paste that offers 
oblique angle views without tilting of the actual board to inspect a 
representative sample of boards will allow you to see
the amount of paste that is located down the holes prior to reflow, 
non-destructively. 

The same test can also be used post reflow to quickly confirm that 
the resultant pin-in-paste hole fill meets the IPC 610D recommendations 
of a minimum of 75% fill. 








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Dr. David Bernard

Product Manager

Dage Precision Industries

Mr. Bernard 
has been the X-ray Systems Product Manager at Dage for over 5 years and 
have been involved in all aspects of x-ray inspection and test for 
printed circuit board assembly applications. Prior
to this, Dr. Bernard was working with radiation measurement 
instrumentation. 


There are numerous tradeoffs to consider when 
pin in paste hole fill is the goal. First, overprinting can be 
problematic due to the possibility of mid chip solder balls. Step 
stencils are more expensive than standard stencils, and will
likely result in reduced throughput and material expense due to the need
 to increase underwipe frequency.



One technology which is becoming very popular is the use of solder 
preforms in tape and reel packaging. The preforms come in standard 
sizes, such as 0402, 0603 and 0805 to name a few. They are packaged 
exactly like chip capacitors and resistors.



Placement is done after paste printing. Only 20-25% of the preform needs
 to contact the solder paste. Since the preform is solid metal, a 
preform as large as four times the volume of the paste volume can be 
added and still achieve perfect reflow results. 







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Paul J. Koep

Global Product Manager

Alpha

Mr. Koep is 
responsible for product planning and technical marketing for the Preform
 Products at Alpha. He is the co-author of several patents in the areas 
of soldering applications focusing on reflow
and alternative methods. 


Reader Comment

Readers may be interested in the free ebook on "Pin In Hole Intrusive Reflow Design and Assembly" at http://www.pihrtechnology.com
 The most common problem with the process is
the hole to lead ratio, at the design stage its easy to change and it 
gives design engineers more tracking space. Changing the hole to lead 
ratio on existing design is easy too as its not going to impact 
reliability either.

Bob Willis, Bobwillisonline.com, UK 






Reader Comment

Going into the reality of pin-in paste requires a little more than 
applying paste into the hole. There are usually unforeseen issues which 
occur after the pin in paste operation. The stencil can be designed to 
prevent inadequate hole fill by forming a
cross pattern with the paste around the top side of the hole. The flux 
will stay mostly on the top of the pcb under the part instead of 
flushing out to the bottom pad. The flowed solder will only take what is
 required to do the job. Making the use of expensive
preforms is not necessary. People are asking for advice or suggestions 
as to which way to perform their particular task at hand. They may not 
be aware of the pitfalls of following this advice. I know I would prefer
 to also know what I shouldn't do as well as
what I should.

Mark A. Maheux Sr., Sr. Manufacturing Engineer, Honeywell Life Safety, USA




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