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Registration techniques for advanced technology PCBs: or, so you think you can really do two-track routing?

This article will review all of the essential steps involved in the proper registration of today's advanced technology printed circuits. We've we've  

Contraction of we have.

we've have
 included a registration template (1) A pre-designed document or data file formatted for common purposes such as a fax, invoice or business letter. If the document contains an automated process, such as a word processing macro or spreadsheet formula, then the programming is already written and embedded in the  that will help PCB PCB: see polychlorinated biphenyl.
 in full polychlorinated biphenyl

Any of a class of highly stable organic compounds prepared by the reaction of chlorine with biphenyl, a two-ring compound.
 manufacturers grade the capabilities within their own factory, and we'll discuss steps needed to improve the aptitude of the systems and processes.

The correct registration and alignment of through-holes, blind and buried bur·y  
tr.v. bur·ied, bur·y·ing, bur·ies
1. To place in the ground: bury a bone.

a. To place (a corpse) in a grave, a tomb, or the sea; inter.

 vias, and soldermask to the innerlayer and outerlayer pads is becoming increasingly difficult with today's tight pitch product, especially on high layer-count boards and/or large form-factor PCs. Include HDI HDI Human Development Index (UNDP yardstick of human welfare)
HDI Help Desk Institute
HDI Humpty Dumpty Institute (New York, New York)
HDI High Density Interconnect
, sequential lamination lamination

a laminar structure or arrangement.
, via-in-pad and other complex design requirements and you assure a challenge to a facility's registration process.

Many producers of PCBs do not fully realize all of the processes that contribute to registering a board for dense-featured ASICs and tight trace spacing. Telecommunication telecommunication

Communication between parties at a distance from one another. Modern telecommunication systems—capable of transmitting telephone, fax, data, radio, or television signals—can transmit large volumes of information over long distances.
 products--with their high layers and large panel sizes--are adding 0.8 mm and 0.5 mm pitch devices into their designs. To improve signal speed and keep the size of the cabinets within spec, they are looking to introduce two-track routing between the BGA/CCGA pads.

The latest movements into dense routing techniques have moved the potential drill-to-metal CAF CAF - constant applicative form  concerns into the forefront, ahead of drill-to-drill CAF potential. Low CAF and non-CAF materials may help with this concern, but these will also increase material costs. In the past, breakout and annular ring annular ring
An opaque area appearing in radiographs of the lung and indicating a cavity of tuberculosis. Also called pleural ring.
 requirements were for holewall reliability concerns. Now the annular ring requirement is an inviolable reference for potential CAF concerns.

Before getting into specific areas of influence, it is important to understand what is involved in registration, specifically innerlayer registration to the primary drill process. The best way to start on a plan of continuous improvement is by bucketing Bucketing

A situation where, in an attempt to make a short-term profit, a broker confirms an order to a client without actually executing it. A brokerage which engages in unscrupulous activities, such as bucketing, is often referred to as a bucket shop.
 each area, then measuring and calculating the influence. Many PCB manufacturers simply add the tolerances of the equipment purchased to complete the registration process and call the rest of the variance The discrepancy between what a party to a lawsuit alleges will be proved in pleadings and what the party actually proves at trial.

In Zoning law, an official permit to use property in a manner that departs from the way in which other property in the same locality
 "material movement."

Some key areas that can influence registration but are frequently ignored are:

The rate of rise monitoring of the PCBs in lamination (not platen A long, thin cylinder in a typewriter or printer that guides the paper through it and serves as a backstop for the printing mechanism to bang into. It is typically made of a hard rubber or rubber-like material. See carriage and typewriter.  temperature). Trying to adjust for scaling influences without monitoring this process creates a constant movement of the material influence target.

Drill depth into backup (small holes). The registration influence can't be measured by a manual caliper caliper

Instrument that consists of two adjustable legs or jaws for measuring the dimensions of material parts. Spring calipers have an adjusting screw and nut; firm-joint calipers use friction at the joint to hold the legs unmoving.
 (visual depth scope), but the drill wander influence can be measured.

Incorrect scaling influences due to scripting errors by CAM cam, mechanical device
cam, mechanical device for converting a rotating motion into a reciprocating, or back-and-forth, motion, or for changing a simple motion into a complex one.
 operators. This is a frequent issue if the entire scaling scripts are not completely automated au·to·mate  
v. au·to·mat·ed, au·to·mat·ing, au·to·mates
1. To convert to automatic operation: automate a factory.

. A small typo typo - typographical error  can change the scaling script to zero, but still show scale values on the film.

Two-camera PEP alignment without slope compensation. The suppliers of this technology have been trying for years to get PCB manufacturers to upgrade, but the old equipment in many shops was purchased used, without much real understanding of the process and limitations. If the targets are offset in one axis (as is the case in the most popular models), then a scaling influence reset is required or a shift will occur. The PEP will not capture this shift.

Hard and soft tooling influences in drilling. While hard tooling has the advantage of being automated, without vision alignment to the drill head, it does add additional variation.

Use of post-lamination x-ray X-ray

Electromagnetic radiation of extremely short wavelength (100 nanometres to 0.001 nanometre) produced by the deceleration of charged particles or the transitions of electrons in atoms.
 systems incorrectly or not understanding resolution vs. accuracy. Trying to register multiple depths of innerlayers at once without understanding what resolution error is involved is a common pitfall pit·fall  
1. An unapparent source of trouble or danger; a hidden hazard: "potential pitfalls stemming from their optimistic inflation assumptions" New York Times.

Lead time after scaling. This must be minimized and consistently controlled, especially in high-heat, high-humidity environments. Frequently, the cores will "grow" with time, and correct scaling today may mean misregistration of the PCB if those cores are allowed to sit for hours or days before processing.

Along with a complete sequencing of each step in the manufacturing process, we can highlight their influences on high-density registration, as well as inform the process engineer of the consequences of using sub-par systems for the task at hand. First, though, we should begin with an understanding of the OEM's registration requirements and the reasoning involved in the specifications.

The first requirement is for accurate registration of the holes to their pads. Usually, there is an annular ring requirement or a spec that at least demands tangency. Advanced technology OEMs demand an annular ring of 1 mil An Internet address domain name for a military agency. See Internet address.

(networking) mil - The top-level domain for entities affiliated with US armed forces.
. This further tightens the registration constraints CONSTRAINTS - A language for solving constraints using value inference.

["CONSTRAINTS: A Language for Expressing Almost-Hierarchical Descriptions", G.J. Sussman et al, Artif Intell 14(1):1-39 (Aug 1980)].
 of the job.

For example: if the design utilizes a 1.00 mm BGA (Ball Grid Array) A popular surface mount chip package that uses a grid of solder balls as its connectors. Available in plastic and ceramic varieties, BGA is noted for its compact size, high lead count and low inductance, which allows lower voltages to be used.  pitch (which typically uses a 10 mil drilled hole on a 19 mil pad), and there is a 1 mil annular ring condition that must be followed, it reduces the hole-to-pad allowances by 2 mils (FIGURE 1).


Many advanced routing designs ignore etch To create a design in a material by digging out the material. The circuit designs on printed circuit boards and chips are etched by acid. See chip and printed circuit board.  compensation with drill-to-metal concerns. (Drill-to-metal refers to the distance from the edge of a drilled hole to the nearest metal feature). Just routing with a 4 mil line doesn't truly achieve the actual drill-to-metal specifics. First, complete the stackup stack·up  
A deployment of aircraft circling an airport at designated altitudes while awaiting instructions to land.
 line width objective, then use that value (with etch compensation) for routing.

Frequently, CAF resistance concerns demand a second necessity for a minimum drill-to-metal spec. With telecom or workstation products, this spec can be as little as 9 to 11 mils (FIGURE 2). If you produce a PCB designed with a drill-to-metal tolerance of 8.5 mils and your registration error is off by as little as 4 mils, the PCB will often be rejected--many OEMs regard a drill-to-metal spacing of 5 mils as a fire hazard fire hazard fire n that's a fire hazard → das ist feuergefährlich

fire hazard n that's a fire hazard → comporta rischi in caso d'incendio 
. This can be extremely difficult to manufacture with large panel sizes.


Another important aspect of registration regarding PCB design is the line width and spacing width between BGA pads for internal routing purposes. For a 1.0 mm BGA device, it is typical to see two-track routing of lines between the pads on internal layers. With today's line and spacing size processing averages of 4/4 for innerlayers, this makes proper registration paramount when building boards with these features (FIGURE 3).


If your registration is off by only 1.5 mils across the panel, then you are close to violating the drill-to-metal constraint Constraint

A restriction on the natural degrees of freedom of a system. If n and m are the numbers of the natural and actual degrees of freedom, the difference n - m is the number of constraints.
 of 8.5 mils. PCB designers would also like to shrink shrink Vox populi noun A psychiatrist  designs down to 0.8 mm pitch devices with two-track routing but, to date, printed circuit suppliers are incapable of producing sub-3 mil lines and spaces. And with today's laminates, they are reticent to build boards with drill-to-metal spacings of less than 7 mils.

TABLE 1 lists all the processes involved in assuring proper registration. Many PCB makers concentrate on only a few of these items, often finding it hard to understand why they cannot significantly improve their registration limitations. To put it bluntly blunt  
adj. blunt·er, blunt·est
1. Having a dull edge or end; not sharp.

2. Abrupt and often disconcertingly frank in speech:
: Pin lamination and accurate punching of the tooling holes are not the end-all to improving registration capabilities. Without giving away any special techniques for registration, simply being able to measure the variance is a huge step in the right direction.

Registration Hot Spots hot spots

acute moist dermatitis.

One of the most difficult changes made at a PCB facility is with the alignment process during any of the innerlayer manufacturing steps. Visual validation See validate.

validation - The stage in the software life-cycle at the end of the development process where software is evaluated to ensure that it complies with the requirements.
 in the outerlayer processes makes the transition much easier. As discussed earlier, innerlayer alignment can still be black magic, so these changes are much slower. Here are some good starting guidelines guidelines, a set of standards, criteria, or specifications to be used or followed in the performance of certain tasks.

1. Automatic scripting of the stackup, core type, scaling details and prepreg materials in a single pick/place Web-based tool eliminates any chances of input error due to reading of stackup data or scaling values by a CAM operator. It also allows the process engineering group to make changes that will now be updated on the next production run.

2. PEP processing is one of the least understood processes in PCB manufacturing. Optimizing all set points and understanding them will create a gate where variation is at least identified before processing. A common method for operating a PEP is to set the offset allowance values (setup See BIOS setup and install program.  and operational) at higher values than the specified tolerance. The common reason for this is that the machine will not punch each board. But isn't this the point of having a screen?

3. Watch for wear on the PEP punches and PEP punches of the wrong size. Each manufacturer has a different strategy for punching the correct size vs. board thickness. Use the recommended method even if it means having three sizes of punches.

4. Use soft tooling for drilling. Except for the optical alignment systems coming soon, nothing gives more repeatable accuracy. Hard tooling, while simple, has multiple registration steps that are reduced when using soft tooling. Be sure to change the soft tooling anytime you remove a pin. Reinserting pins defeats the reason for using soft tooling.

5. Measure drill depth on every setup. This should be done on the smallest drill size. Using an optical measuring device is the best method. Cross-section also works, but it's slow. Pin devices on 10 mil holes are a waste of time.

6. Measure every load laminated laminated /lam·i·nat·ed/ (-nat?ed) having, composed of, or arranged in layers or laminae.


made up of laminae or thin layers.
 for the rate of rise (R of R). Use a wireless thermocouple with a PC interface to reduce the danger of running this test. Getting scaling data without understanding the R of R influence is like chasing a moving target.

7. Use a control depth visual measuring device to measure scale influence; do not rely on electrical circuit or x-ray systems for rounded up data. Available advanced registration systems give excellent data at the pre-drill tooling step.
TABLE 1. Key +/- 3.5 mils Innerlayer Registration Template

                                                KEY REGISTRATION
PROCESS                 ITEM                    VARIABLE

Front-end engineering   I/L core scaling        Core thickness,
completely automated                            construction and grain
Artwork                                         direction
                        I/L core scaling        Signal/plane/mixed
                                                layout with facing
                                                prepreg type
                        Film stabilization      Film environment
                        Plotter environment     Environment temp and RH
                        Plotter accuracy        X/Y dimension and
                                                feature definition auto
                                                scripting of
                        Film coating            Film tension influence,
                                                or don't use
                        A/W accuracy            X/Y dimension and
                                                feature definition per
Standardized core       Material stability      Laminate dimensional
material                                        stability as received
I/L Imaging and etch    Imaging environment     Temp and RH
include setup in each   Core resist laminated   Lam temperature before
evaluation              temp                    exposure
                        A/W exposure            Film dimension check,
                                                X/Y, before setup
                        A/W exposure            Film exposure limits
                                                during HVM
                        A/W exposure            Film exposure limits
                                                life of film
                        I/L image alignment     Top to bottom
                        Core handling.          Stacking height, X/Y
                        pre-DES                 dimension
                        Post DES core           Stacking height, X/Y
                        handling                dimension
I/L post-etch punch     I/L punch target        I/L target X/Y
includes setup in       dimension               dimension
each evaluation         Punch diameter          Punch hole dimension
                        PEP punch accuracy      Punch hole true
                                                position, all locations
                        PEP punch alignment     Punch hole to I/L
                                                target difference, X/Y
                        PEP punch               X/Y difference based on
                        repeatability           HVM Lot data
Oxide                   Core drying             X/Y dimension
Lamination              Caul plate bushing      Bushing dimension
                        Pin size                Pin dimension
                        Lay-up skew             I/L core movement on
                                                pins, X/Y rotations
                        Rate of rise            Lam book temp vs. stack
                                                height and lagging
                        Press cycle             Total press opening/
                                                book ramp rate and
                                                delta, with procedural
                                                recommendations if
                        Press cure              Laminated book cure, Tg
                        X-ray target drill      Feature recognition by
                        resolution              lam thickness and
Include setup in each   X-ray target drill      Target drill hole true
evaluation              accuracy                position, X/Y
                        X-ray target drill      Target drill hole to
                        alignment               I/L target
                                                registration, X/Y
                        X-ray target drill      X/Y registration
                        repeatability           profile, based on HVM
                                                Lot data
                        I/L scale measuring     Optek/measuring feature
                        data, resolution        recognition by lam
                                                thickness /location
                        I/L scale measuring     Optek/measuring
                        data, accuracy          accuracy by lam
                                                thickness / location
                        I/L scale measuring     Measuring repeatability
                        data, repeatability     by lam thickness/
Drill                   Drill tooling pins      Pin diameter
                        Drill table true        Spindle to table true
                        position                position
                        Drill pinning           Verification of tooling
                        alignment               pin Alignment / true
Include setup in each   Drill run-out           Dynamic spindle run-out
evaluation              Drill hole true         Drill feeds/speeds and
                        position                depth
                        Drill bits              Drill bit usage new,
                                                re-sharps, hits
                        Drill pattern           Validation of X/Y
                        inspection              locations and shape
                                                after drill
O/L Image               O/L image               O/L to drill alignment
SM Image                SM image registration   SM to O/L alignment

MIKE BARBETTA is a consultant with over 27 years in the industry. Previously, he has worked for Cisco Systems “Cisco” redirects here. For other uses, see Cisco (disambiguation).
Cisco System,Inc. (NASDAQ: CSCO, HKSE: 4333 ) is an American multinational corporation with 54,000 employees and annual revenue of US $28.48 billion as of 2006.
, PCB suppliers and chemical vendors, with experience in process engineering, technical service, engineering management and global supply management. He can be reached at JOE DICKSON Joe Dickson is a Canadian politician. He was elected to the Legislative Assembly of Ontario in the 2007 provincial election, representing the riding of Ajax—Pickering. He is a member of the Liberal Party.  is manager of the PCB SupplierTechnology Group in Hardware Reliability at Cisco Systems. He has over 30 years of PCB engineering management experience, formerly serving as director of technology for Tyco Electronics Tyco Electronics was the largest unit of Tyco International Ltd., and the world's leading supplier of passive electronic components. On June 29, 2007 Tyco Electronics became a wholly independent publicly-traded company, along with Covidien, from the breakup of the Tyco conglomerate , Sigma SIGMA - A scientific visual programming environment from NASA.
 Circuits and SBC (1) (SBC Communications Inc., San Antonio, TX, A large, national telecommunications company that grew from a multitude of local and regional companies, including Southwestern Bell, Pacific Bell and Nevada Bell, into a single, unified brand by 2002. .
COPYRIGHT 2004 UP Media Group, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
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Title Annotation:Drilling
Author:Dickson, Joe
Publication:Printed Circuit Design & Manufacture
Date:Dec 1, 2004
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