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Bill Coleman
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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.

Bill Coleman has submitted responses to the following questions.
Recommended Solder Paste Aperture Configuration
008004 .004 x .005 oblong with .003 space 01005 .005 x .006 oblong with .004 space ...
What Is Causing Connectors to Bow?
Here is my idea: Pins on connector fit tight it holes, At elevated temperature of wave the connector bows because ...
Problems With Large Voids
I have 2 suggestions Reduce the solder paste printed on the ground plane with window pane apertures letting the volatiles ...
Initial Screen Print Test Board
Yes. Good practice. ...
Stencil Pattern for Thermal Pads on QFNs
Recommended aperture design for QFN thermal pads is 40-50% reduction of paste printed using window pane pattern. Also to try ...
Calculating PCB Hole Diameters
Pin to Hole ratio is important in Intrusive Reflow. The attached shows Pin to hole ratio ranging from .52 to ...
LED Component Shift During Reflow
Shift can result from insufficient channels for out gassing of the solder paste vehicles during reflow. One way to correct ...
How Many Fiducials Pre Solder Paste Stencil?
Typically 3 are sufficient. ...
MELF Component Misalignment
In my opinion the glue in the middle of the MELF being raised is acting like a see-saw causing instability ...
Options for Reballing BGA Components
I would recommend re-balling by applying flux first then solder balls. No need to change process depending on ball size. ...
Test Probe Problems After Pin-In-Paste
Suggest reducing the volume of solder paste. This should reduce flux residue.  As a reference see "Intrusive Reflow of Lead ...
Automatic Insertion Causing Plated Hole Damage
Intrusive reflow could solve the problem. Board would need to be redesigned for non-press fit holes. ...
Step Stencil Question
Pressure is set to achieve clean wipe of solder paste as in normal SMT printing. However there will be some ...
Through Hole Connector Solder Joint Hole Fill
X-Ray inspection works very well for inspecting for voiding and fillet fill. ...
Pin-in-Paste Standards
In order to prevent the pin from pushing paste out of the through hole, the length should not be much ...
Insufficient Barrel Fill on Through-hole Components
I only have experience with Intrusive reflow pin in hole. In this case too big of a pin to hole ...
Glued SMT Components Falling Off
Suggest you check the thickness of the stencil and the stand-off distance of the Capacitors vs. the resistors. Maybe the ...
Stencil Design Guidelines
IPC is releasing rev B of 7525. This as well as stencil vendor guidelines are used in the industry ...
Contract Assembly in a Prison
There are tools that hold the parts while you hand print solder paste on the package. Then place this part ...
Stencil Life
Oversimplified recommendation: When you can't get a clean paste wipe at any pressure--replace the blades When the stencil is loose ...
Stepped Stencil Limit
IPC 7525 recommends 35 to 50 mils keep-out for each 1 mil of step. ...
Minimum Solder Sphere Count Per Pad
Design guide for stencil aperture size (IPC 7525) is least 5 solder balls across the aperture opening. ...
Stencil Tension
What is more important is the tension of the stencil itself. As it is used it the stencil foil may ...
Nano Coated Stencil Wear
Good questions I know of no way a user can measure the nanocoat thickness since some nanocoats are only nonometers ...
Solder Mask Stencil Tension
Four Points (772-288-3271) showed a device for measuring stencil tension at the recent APEX Exhibit. ...
Opens at BGA Component Corner Balls
Have you tried making the stencil aperture larger for the 4 corners? ...
Stencil Issue with PLCC Component
Have you tried making the stencil aperture larger in heel area maybe overprinting by 10 to 30 mils? ...
Uncontrolled Environment Causing Problems
What is the aperture size and stencil thickness? Is the area ratio > .66? ...
Square vs. Round
Click here to see the results of a test comparing paste release from round and square apertures. E-FAB (Electroformed); L-A (laser-cut ...
Most Important Factors for Screen Printing
Both paste volume and print alignment are critical parameters in the printing process. IPC 7525 rev A suggest .1 mils ...
Guidelines for Pin-in-Paste
I have a Through Hole stencil design guideline that we use to make stencils for intrusive reflow stencil customers. Input ...
Solder Paste Volume
Normally you want to put enough paste on the stencil that it forms a bead in front of the squeegee ...
Problems with Insufficient Barrel Fill
George Oxx and I published the results of testing we performed on Lead-Free Intrusive Reflow which showed good barrel fill. ...
Leadless Component Hand Soldering Help
You may want to check out Photo stencil QFN/BGA Repair tool ...
Issues with BGA Components Near PCB Edges
If your printer has board edge clamps you may need to put a relief pocket on bottom side of the ...
Wave soldering of fine pitch through hole components
The article can be found in an of SMT Magazine titled Intrusive Reflow of Lead-Free Solder Paste. ...
How to Clamp Odd Shaped Circuit Boards
From a stencil viewpoint when the claps are too close to apertures the stencil can not gasket to the board ...
Recommended lead to hole ratio
In a study on "Lead Free Intrusive Reflow," SMT Magazine Nov and Dec 2007, we found that a pin to ...
Pin-in-Paste Hole Fill
Same paste should work. You can calculate amount of paste required knowing 4 items: pin dimension, board thickness, hole size, ...
Type III vs. Type IV solder paste
The normal rule of thumb is the stencil aperture should be at least 5 times the average solder sphere in ...
Reflow BGA's with CSP's
Couple of ways to approach this problem. Design the boards w/o via in BGA pads Overprint the BGA pad with ...
BGA Rework
Seems like a difficult task. There is another option for reworking BGA's and that is to print solder paste on ...
Solder bridging on BGA's
From a stencil printing perspective bridging can be the result of a poor print (poor stencil) or a good print ...
Type IV solder paste on 0201
Type 4 would be the paste of choice for 0201 applications. Rule of thumb is the stencil aperture size should ...
Part Movement During Reflow
Suggest you look at IPC 7525 for aperture recommendations on the ground plane. Window pane aperture at about 50% area ...
BGA Rework - with or without solder paste
My input is for Tin Lead applications flux should work OK for tinned pads, but for Lead Free you want ...
SMT adhesive problems after wave solder process
I don't know if you are dispensing or printing glue but there are advantages to stencil printing. There is much ...
BGA re-balling process
Photo Stencil offers a Universal BGA repair tool. The tool holds the BGA package in place with a ball drop ...
Tombstone problems
One solution is to paste and glue the chip components. This is done in a two print process where paste ...
Stencil printing process problems
Squeegee blades can make a difference as far as curtaining. Suggest you look at DuraGlide squeegee blades and see if ...
Through-hole ratios for PCB's
We ran some recent tests and reported at APEX 06 "Lead Free Intrusive Reflow" by Coleman and Oxx. In this ...
Lead-free bar solder for wave soldering
Can't help with the solder bar issue but Lead Free Intrusive Reflow is a process which eliminates the need for ...
Screen printing QNF24 problem
The latest revision of IPC 7525 Stencil Design Guidelines deals with QFN stencil aperture design. Specifically it is recommended to ...
Lead-free soldering problem
Answer to Question 1 Could be that there is a solder wetting issue or a coplanarity issue. Those seem to ...
0201 capacitors creating process problem
We have run several comparison tests between different stencil technologies (AMTX Electroform and Laser-Cut) for Lead-Free solder paste. We fine ...
Reflow of "high-lead" flip chip device
Years ago we supplied a stencil where they put an eutectic cap on the high-lead balls. The stencil had small ...
Problems with solder paste stencils
Normally it is a good design guide to have the area Ratio above .66 for Laser-Cut stencils. The normal aperture ...
Can we convert our existing wave soldering machine to use lead free?
One alternative is Intrusive reflow which eliminated the need for Wave soldering all together. I have attached a technical paper ...
Problems with defect BGA connections on large BGA's and on ENIG plated boards
You may want to try a step up stencil in the BGA area; step up to 8 mil thick. This ...
Advise and suggestions for assembly using 01005 capacitors.
01005 are very small components with small pads. Area Ratio is less than .66 which is required for good paste ...